Category Archives: Deep South

GOES-16 IFR Probabilities in AWIPS

Visible Imagery and GOES-16 IFR Probability Fields, 2202 UTC on 29 November 2017 (Click to enlarge)

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

GOES-16 IFR Probabilities can now be displayed in AWIPS.  This site has included the product for several months now.  The imagery above, however, is from AWIPS, showing a toggle between Visible GOES-16 Imagery (with and without observations of ceiling heights and visibilities), MVFR (Marginal Visible Flight Rules) Probabilities, IFR (Instrument Flight Rules) Probabilities and LIFR (Low Instrument Flight Rules) Probabilities.  GOES-16 IFR Probability fields are Bayesian and have been trained using about 2 months’ worth of GOES-16 Data.  The LDM data feed will be providing data once GOES-16 Data are flowing again, sometime between 14 December and 20 December, when GOES-16 is on station at 75.2 º W Longitude.

GOES-16 IFR Probability, 0642-1137 UTC on 30 November 2017 (Click to enlarge)

Dense Fog covered parts of Florida early on 30 November, and the animated GOES-16 IFR Probability field, above, shows the benefit of GOES-16’s routine 5-minute temporal cadence:  the motion of the fog field is well-captured, and it’s straightforward to use the field to estimate the onset of IFR conditions.  The Advanced Nigthtime Microphysics RGB for the same time period is shown below, and that product does not well indicate the widespread nature of the reduced ceilings and visibilities over northern Florida.

GOES-16 Night-time Microphysics RGB, 0642-1137 UTC on 30 November 2017 (Click to enlarge)

Screen Capture for http://www.weather.gov at 1148 UTC on 30 November 2017 (Click to enlarge)

Dense Fog Advisories were widespread over the southeastern US on the morning of 30 November, as shown by the screen capture above, from 1148 UTC 30 November. The toggle below shows IFR Probabilities and the Advanced Microphysics RGB for 1147 UTC on 30 November.  The 10.3 µm – 3.9 µm Brightness Temperature Difference (BTD) for the same time shown at the bottom. Evidence of multiple cloud decks is apparent in the image. Such mid- and high-level clouds result in an ambiguous signal as far as fog detection goes in both the BTD and in the RGB. IFR Probabilities give a consistent signal in those regions that relies on Rapid Refresh Model output suggesting low-level saturation is present.

GOES-16 IFR Probabilities and the GOES-16 Advanced Microphysics RGB at 1147 UTC on 30 November 2017 (Click to enlarge)

GOES-16 Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), 1147 UTC on 30 November 2017 (Click to enlarge)

Dense Fog Advisories over Memphis

Dense Fog Advisories were issued over Memphis and adjacent portions of the mid-south on Tuesday morning, 7 November. (Click here for a 1230 UTC screen capture from the Memphis National Weather Service webpage). The Advisory text is at the bottom of the post.

GOES-16 Brightness Temmperature Difference field (10.3 µm – 3.9 µm) from 0502 through 1252 UTC on 7 November 2017 (Click to enlarge)

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

GOES-R IFR Probabilities are computed using Legacy (Operational) GOES (GOES-13 and GOES-15) and Rapid Refresh model information; Preliminary IFR Probability fields computed with GOES-16 data are available here. IFR Probability fields based on GOES-16 will be available via LDM Request when GOES-16 becomes operational as GOES-East (currently scheduled for some time between 11 and 20 December 2017).

The animation above shows the GOES-16 Brightness Temperature Difference Product (at every 10 minutes, rather than the typical 5-minute temporal cadence of GOES-16 over the continental US) during the night on 7 November.  In the default color enhancement shown, clouds made up of water droplets are show up as cyan and blue whereas higher clouds are black.  Note also the effects of increasing solar reflectance at the end of the animation:  the brightness temperature difference is switching sign as increasing amounts of 3.9 µm radiation are reflected off the clouds.

It could be difficult to use the animation above, alone, to heighten situational awareness of a developing region of fog because of the confounding effects of higher clouds.  Additionally, infrared satellite imagery is challenged to detect cloud thickness:  are the stratus clouds detected (cyan/blue in the enhancement) mid-level, low-level or both?

IFR Probability fields can screen out regions of mid-level stratus, regions that are not so important from the point of view of transportation.  This is because Rapid Refresh Model output is used as a predictor in the statistical model underlying IFR Probability fields.  If the Rapid Refresh Fields do not show low-level near-saturation, the IFR Conditions are less likely.

Consider, for example, the animation below of IFR Probability fields computed for GOES-13 data.  At the beginning of the animation, the fields clearly distinguish between regions where dense fog is occurring near Memphis, and where mid-level stratus is more common (over northern Mississippi).  As dawn approaches, reports of fog become more widespread over Mississippi — but the product has given a timely alert to how conditions might differ over a short region that was not possible with the single brightness temperature difference product alone.

GOES-13 IFR Probability fields, hourly from 0315-1215 UTC on 7 November 2017 (Click to enlarge)

GOES-R IFR Probabilities are available via an LDM feed to National Weather Service Offices. At present, IFR/Low IFR and Marginal IFR Probabilities (and Cloud Thickness) fields that are sent are those created by the operational GOES-East Satellite, GOES-13.  IFR Probability Products based on GOES-16 are being produced now, however, and are available here. The short animation below shows a behavior similar to the product based on GOES-13, but GOES-16 has far better temporal and spatial resolution!  Click here for a toggle between GOES-13 IFR Probabilities, GOES-16 Brightness Temperature Difference Fields, and GOES-16 IFR Probabilities at 0715 UTC.

When GOES-16 is operational as GOES-East, currently scheduled to occur between 11 and 20 December 2017, the LDM feed will supply GOES-East IFR Probabilities computed with GOES-16 data.

GOES-16 IFR Probabilities, 0402-0557 UTC on 7 November 2017 (Click to enlarge)

Suomi NPP flew over the region at 0740 UTC on 7 November, and there was ample illumination to see the clouds. Multiple cloud decks and levels are apparent below.

Suomi-NPP Day Night Visible Imagery (0.70 µm) Near-Constant Contrast Product, 0741 UTC on 7 November 2017 (Click to enlarge)

URGENT – WEATHER MESSAGE
National Weather Service Memphis TN
1228 AM CST Tue Nov 7 2017

…A Dense Fog Advisory is in Effect for Portions of the Midsouth
including the Memphis Metro Area…

ARZ036-048-049-MSZ001>004-007-008-TNZ088>090-071500-
/O.EXT.KMEG.FG.Y.0025.171107T0700Z-171107T1500Z/
Crittenden-St. Francis-Lee AR-DeSoto-Marshall-Benton MS-Tippah-
Tunica-Tate-Shelby-Fayette-Hardeman-
Including the cities of West Memphis, Forrest City, Marianna,
Southaven, Olive Branch, Holly Springs, Ashland, Ripley MS,
Tunica, Senatobia, Bartlett, Germantown, Collierville, Memphis,
Millington, Somerville, Oakland, and Bolivar
1228 AM CST Tue Nov 7 2017

…DENSE FOG ADVISORY NOW IN EFFECT UNTIL 9 AM CST THIS MORNING…

* VISIBILITY…Less than one-half mile.

* TIMING…Through 9 AM CST Tuesday.

* IMPACTS…Dense fog will most commonplace outside of the
Memphis urban center and near bodies of water. Travel may
become difficult due to limited visibilities.

PRECAUTIONARY/PREPAREDNESS ACTIONS…

A Dense Fog Advisory means visibilities will frequently be
reduced to less than one quarter mile. If driving…slow down…
use your low beam headlights…and leave plenty of distance ahead
of you.

&&

$$

JAB

Dense Fog over Missouri and over Alabama

GOES-R IFR Probability Fields, Hourly from 0215-1315 UTC on 19 September 2017 (Click to enlarge)

GOES-R IFR Probabilities are computed using Legacy GOES (GOES-13 and GOES-15) and Rapid Refresh model information; GOES-16 data will be incorporated into the IFR Probability algorithm in late 2017

Dense fog developed over Missouri on Tuesday 19 September and Dense Fog Advisories were issued. The animation above shows the hourly development of GOES-R IFR Probability fields; values increased from northern Missouri to southern Missouri as dense fog developed, first north of I-70, then south into the rest of the state. The morning of 19 September was mostly devoid of mid-level and high-level clouds over Missouri (exception: west-central Missouri starting after 0900 UTC), and that kind of night means that traditional methods of fog detection work well. The brightness temperature difference field between the shortwave Infrared and the Longwave Infrared (3.9 µm and 10.3 µm on GOES-16, 3.9 µm and 10.7 µm on GOES-13) shows the fog development.

Note that the IFR Probability field, above, does not show fog dissipating around sunrise. That’s in contrast to the Brightness Temperature Difference field below. As the sun rises, the amount of solar radiation at 3.9 µm that is reflected off the clouds increases; this changes the brightness temperature difference from positive (cyan in the color enhancement shown) to negative (grey or black in the enhancement shown).

GOES-16 has better spatial resolution than GOES-13; thus, the small valley fogs that can develop in the rugged (ish) terrain of southern Missouri are resolved in GOES-16, but not in GOES-13. When GOES-R IFR Probability is created using GOES-16 data (slated to begin in late 2017), the resolution improvements in GOES-16 will migrate to IFR Probability fields.

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing.

GOES-16 Brightness Temperature Difference (10.3 µm – 3.9 µm), hourly from 0412 to 1112 UTC on 19 September (Click to enlarge)


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On 20 September, Dense Fog developed over Tennessee and Alabama, leading to the issuance of Dense Fog Advisories. The GOES-R IFR Probability field, below, shows good agreement between high probabilities and reduced ceilings/visibilities.

GOES-R IFR Probability Fields, Hourly from 0415-1315 UTC on 20 September 2017 (Click to enlarge)

As on the 19th over Missouri, top, this was a night with relatively few middle- and upper-level cloud decks. On such nights, the GOES-16 Brightness Temperature Difference field can capably identify regions of stratus (it’s up to a human to decide if the stratus deck extends to the surface; on this night, much of the stratus did). The 2-hour animation of Brightness Temperature Difference, below, highlights two particular strengths of GOES-16: Better spatial resolution that allows small valleys to be sampled correctly, and good temporal resolution (every 5 minutes vs. every 15 minutes for GOES-13) that allows superior monitoring of the cloud evolution with time. Note that the rising sun is eroding the GOES-16 Brightness Temperature Difference signal by the end of the animation below.

GOES-16 Brightness Temperature Difference (10.3 µm – 3.9 µm), hourly from 1002 to 1202 UTC on 20 September (Click to enlarge)

The Brightness Temperature Difference field (10.3 µm – 3.9 µm) is a key component to the Nighttime Microphysics Red/Green/Blue Composite. As the toggle below shows, the Brightness Temperature Difference field overwhelmingly controls the region identified by the RGB as one with a potential for fog.

Dense Fog under high clouds in the Deep South

GOES-13 Brightness Temperature Difference (3.9 µm – 10.7 µm) Values at 0815 UTC on 23 May 2017 (Click to enlarge)

Note: GOES-R IFR Probabilities are computed using Legacy GOES (GOES-13 and GOES-15) and Rapid Refresh model information; GOES-16 data will be incorporated into the IFR Probability algorithm in late 2017

The legacy method of detecting fog/low clouds from satellite is the Brightness Temperature Difference product that compares computed brightness temperatures at 3.9 µm and at 10.7 µm. At night, because clouds composed of water droplets do not emit 3.9 µm radiation as a blackbody, the inferred 3.9 µm brightness temperature is colder than the brightness temperature computed using 10.7 µm radiation. In the image above, the brightness temperature difference has been color-enhanced so that clouds composed of water droplets are orange — this region is mostly confined to southeast Texas. Widespread cirrus and mid-level clouds are blocking the satellite view of low clouds. IFR and near-IFR conditions are widespread over east Texas, Louisiana and Mississippi. The GOES-R IFR Probability field, below, from the same time, suggests IFR conditions are likely over the region where IFR conditions are observed.

This is a case where the model information that is included in this fused product (that includes both satellite observations where possible and model predictions) fills in regions where cirrus and mid-level clouds obstruct the satellite’s view of low clouds.. As a situational awareness tool, GOES-R IFR Probability can give a more informed representation of where restricted visibilities and ceilings might be occurring.

IFR Conditions continued into early morning as noted in this screenshot from the Aviation Weather Center.

GOES-R IFR Probability fields, 0815 UTC on 23 May 2017 (Click to enlarge)

Dense Fog along the Florida Gulf Coast

GOES-R IFR Probability Fields, hourly from 0415-1107 UTC on 17 April 2017 (Click to enlarge)

Note: GOES-R IFR Probabilities are computed using Legacy GOES (GOES-13 and GOES-15) and Rapid Refresh model information; GOES-16 data will be incorporated into the IFR Probability algorithm in late 2017.

GOES-R IFR Probability fields, above, show increases in IFR Probability starting around midnight local time. The IFR Probability fields generally outline the regions where fog occurred (and which led to the issuance of dense fog advisories to the east of Mobile). How did the brightness temperature difference field capture this event? Brightness Temperature Difference fields have been used historically to identify regions of stratus.

GOES-13 Brightness Temperature Difference fields (3.9 µm – 10.7 µm), hourly from 0415-1107 UTC on 17 April 2017 (Click to enlarge)

The brightness temperature difference field, above, shows a slow increase in negative values (negative because the brightness temperature computed from emitted 3.9 µm radiation is cooler than that computed from emitted 10.7 µm radiation over clouds composed of water because such clouds do not emit 3.9 µm radiation as a blackbody), but careful inspection of the field shows IFR conditions in regions outside the largest signal (highlighted in this enhancement in yellow).  This occurs mostly were cirrus clouds are indicated (represented as dark regions in the enhancement, over central Mississippi, for example).  In such regions, the IFR Probability fields can maintain a signal of IFR conditions because low-level saturation is predicted by the Rapid Refresh Model.

This fused product combines the strengths of both inputs:  Satellite detection of low clouds, and model prediction of low-level saturation.

As the sun rises, the amount of reflected solar radiation at 3.9 µm increases, and the sign of the brightness temperature difference changes from negative at night over water clouds to positive.  This toggle below shows the brightness temperature difference at 1107 and 1145 UTC.  The decrease in signal does not necessarily mean fog is decreasing.

GOES-13 Brightness Temperature Difference fields (3.9 µm – 10.7 µm) at 1107 UTC and 1145 UTC on 17 April 2017 (Click to enlarge)

A toggle of the IFR Probability and the Brightness Temperature Difference at 1145 UTC, below, shows that the IFR Probability fields can maintain a useful signal during the time of rapid changes in reflected solar radiation with a wavelength of 3.9 µm.

GOES-R IFR Probability and GOES-13 Brightness Temperature Difference fields (3.9 µm – 10.7 µm) at 1145 UTC on 17 April 2017 (Click to enlarge)

Dense Fog in Louisiana

GOES-R IFR Probabilities computed using GOES-13 and Rapid Refresh Data, 0400-1000 UTC on 20 March 2017 (Click to enlarge)

Note: GOES-R FLS products are currently derived from GOES-13 and GOES-15 data. A GOES-16 version of the GOES-R FLS products will not be available until later in 2017.

Dense Fog advisories were issued for much of central and southern Louisiana (screenshot taken from this site) on Monday morning, 20 March 2017;  IFR and Low IFR conditions were widespread (screenshot from this site).  The animation above shows the development of IFR Probabilities in concert with the development of IFR conditions. A strength of the IFR Probability field on this day was that it indicated the possibility of fog development some time before satellite brightness temperature difference fields. Low-level saturation was (correctly) occurring in the Rapid Refresh model, and that helped increase IFR Probability values.

Consider the toggle below, showing, the IFR Probability and Brightness Temperature Difference fields at 0500 UTC. The Brightness Temperature Difference field over coastal Louisiana at 0500 shows little indication of fog development. An animation brightness temperature difference fields that matches the 0400-1000 UTC timeframe shown above for IFR Probabilities is below. Although a strong brightness temperature difference signal is present in Texas, it does take some time for the signal to develop over Louisiana. IFR Probabilities were more helpful for situational awareness on this day.

IFR Probabilities and GOES-13 Brightness Temperature Difference Fields (3.9 µm – 10.7 µm), 0500 UTC on 20 March 2017 (Click to enlarge)

GOES-13 Brightness Temperature Difference (3.9 µm – 10.7 µm), 0400-1000 UTC on 20 March 2017 (Click to enlarge)

Dense Fog Advisories along the western Gulf Coast

GOES-R IFR Probability fields, hourly from 0145-1345 UTC on 08 February 2017, along with surface observations of visibility and ceiling height (Click to enlarge)

Dense Fog developed along the western Gulf Coast early on the morning of 8 February 2017, leading to the issuance of Dense Fog Advisories (graphic from this site) and of IFR Conditions (graphic from this site).  The animation above shows the expansion of the field of high IFR Probabilities northwestward from the Gulf of Mexico starting at 0145 UTC.  IFR Conditions reported in concert with the arrival of higher IFR probabilities.  Relatively high IFR Probability values also develop over northern MIssissippi and Alabama.

The traditional method of detecting low clouds at night, the brightness temperature difference field computed using brightness temperatures at 3.9 µm and 10.7 µm detects water-based clouds because of the different emissivity properties of the water-based cloud at those two wavelengths.  If ice clouds (at high levels) or mixed phase clouds (at mid-levels) exist, however, the satellite cannot view the low clouds.  This was the case on 8 February over northern Mississippi and northern Alabama, and also occasionally over Louisiana and Texas.  The toggle below from 0945 UTC, between the GOES-R IFR Probability field and the Brightness Temperature Difference field, shows several regions where Brightness Temperature Difference field enhancements do not indicate low clouds (over northwestern Mississippi, for example); in these regions, IFR Probabilities are nevertheless large because Rapid Refresh model data shows saturation in the lowest 1000 feet of the atmosphere, strongly suggestive of high IFR Probabilities, and that predictor serves to increase the value of the IFR Probability. The animation of the Brightness Temperature Difference fields is at the bottom of this blog post; compare it to the IFR Probability fields at the top. The IFR Probability algorithm capably fills in regions under high clouds/mid-level clouds where the satellite cannot view low clouds.  It gives a more consistent (and more accurate) depiction of the spread of the low clouds/fog.

Brightness Temperature Difference (3.9 µm – 10.7 µm) and GOES-R IFR probability at 0945 UTC on 8 February 2017 (Click to enlarge)

Another difficulty with Brightness Temperature Difference fields occurs around sunrise when increasing amounts of reflected solar radiation at 3.9 µm cause a sign change in the brightness temperature difference field (reflected 3.9 µm radiation increases as the sun rises and the computed brightness temperature therefore changes because reflected solar radiation at 10.7 µm is minimal;  emissivity-related differences between the two bands are overwhelmed).  The toggle below compares 1245 UTC and 1345 UTC Brightness Temperature Values.

Brightness Temperature Difference (3.9 µm – 10.7 µm) at 1245 and 1345 UTC on 8 February 2017 (Click to enlarge). Decreases in the brightness temperature differences occur at 1345 UTC because of increases in reflected solar radiation at 3.9 µm.

Brightness Temperature Difference (3.9 µm – 10.7 µm), 0145 – 1345 UTC on 8 February 2017, along with surface observations of ceilings and visibility (Click to enlarge)

IFR Conditions across the Deep South

GOES-R IFR Probability computed with GOES-13 and Rapid Refresh Model Data, hourly from 0215 through 1415 UTC on 20 December 2016 (Click to enlarge)

Widespread IFR Conditions developed across Mississippi, Alabama, Georgia and neighboring states on Tuesday morning 20 December, as evidenced by the Aviation Weather Center website screen grab at the bottom. GOES-R IFR Probabilities captured the evolution of the low ceilings and reduced visibilities. In particular, note in the animation above the westward progress of the higher IFR probabilities through Mississippi; IFR conditions develop at, for example, Jackson (KJAN), Greenwood (KGWO) and Oxford (KUOX) as the high probabilities move over the station. Its motion was useful as a forecast tool on this morning.

The GOES-R IFR Probability field has noticeable stripes in it at the end of the animation.  This occurs because high clouds have overspread the low stratus/fog.  When that happens, satellite data can no longer be used as a predictor in the IFR Probability algorithm because the satellite can no longer view the low clouds;  Rapid Refresh data alone are driving the values.  The toggle between the brightness temperature difference field (3.9 µm – 10.7 µm) and the IFR Probability field, below, from 1115 UTC on 20 December, shows the effect.  Where fog/stratus are present (yellow in the enhancement used for the brightness temperature difference field), IFR Probability values are larger because satellite and model data can be used to compute IFR Probability.  Where high clouds are present (dark grey in the brightness temperature difference enhancement), only Rapid Refresh data can be used.

GOES-R IFR Probability and GOES-13 Brightness Temperature Difference (3.9 µm – 10.7 µm) fields, 1115 UTC on 20 December 2016 (Click to enlarge)

Aviation Weather Center website screengrab, 1443 UTC on 20 December 2016 (Click to enlarge)

Dense Fog in Georgia and Florida

ifrprob_25nov2016_0000_1300anim

GOES-R IFR Probability Fields, 0000 – 1300 UTC on 25 November 2016 (Click to enlarge)

Light winds and a long November night allowed radiation fog formation over much of the deep south early on 25 November 2016. (1200 UTC Surface analysis is here). The Aviation Weather Center Website indicated widespread IFR Conditions, below, over the south, with the sigmet suggesting improving visibilities after 1400 UTC.

The animation above shows the evolution of the GOES-R IFR Probability fields from just after sunset to just after sunrise. There is a good spatial match between observed IFR conditions and the developing field. IFR Probability can thus be a good situational awareness tool, identifying regions where IFR Conditions exist, or may be developing presently.

awc_1400utc_25nov2016_ifr

Screenshot of Aviation Weather Center Front Page, 1405 UTC on 25 November (Click to enlarge)

Did the GOES-13 Brightness Temperature Difference Field identify the fields? The animation below, from 0200-1300 UTC, shows a widespread signal that shows no distinguishable correlation with observed IFR conditions.  Note also how the rising sun at the end of the animation changes the difference field as more and more reflected solar radiation with a wavelength of 3.9 µm is present.  In addition, high clouds that move from the west (starting at 0400 UTC over Louisiana) prevent the satellite from viewing low clouds in regions where IFR conditions exist.

btd_25nov2016_0200_1300anim

GOES-13 Brightness Temperature Difference field (3.9 µm – 10.7 µm), 0200-1300 UTC on 25 November 2016 (Click to enlarge)

The high clouds that prevent satellite detection of low clouds, as for example at 1100 UTC over parts of Alabama, cause a noticeable change in the IFR Probability fields, as shown in the toggle below.  Values over the central part of the Florida panhandle are suppressed, and the field itself has a flatter character (compared to the pixelated field over southern Georgia, for example, where high clouds are not present).  Even though high clouds prevent the satellite from providing useful information about low clouds in that region, GOES-R IFR Probability fields can provide useful information because of the fused nature of the product:  Rapid Refresh information adds information about low-level saturation there, so IFR Probability values are large.  In contrast, over southern Florida — near Tampa, for example, Rapid Refresh data does not show saturation, and IFR Probabiities are minimized even through the satellite data has a strong signal — caused by mid-level stratus.  Soundings from Tampa and from Cape Kennedy suggest the saturated layer is around 800 mb.

ifr_btd_25nov2016_1100toggle

GOES-R IFR Probability fields and GOES-13 Brightness Temperature Difference Fields, 1100 UTC on 25 November 2016 (Click to enlarge)

GOES-R Cloud Thickness, below, related 3.9 µm emissivity to cloud thickness via a look-up table that was generated using GOES-West Observations of marine stratus and sodar observations of cloud thickness. The last pre-sunrise thickness field, below, is related to dissipation time via this scatterplot. The largest values in the scene below are around 1000 feet, which value suggests a dissipation time of about 3 hours, or at 1445 UTC.

cloudthickness_25nov2016_1145

GOES-R Cloud Thickness Field, 1145 UTC on 25 November 2016 (Click to enlarge)

IFR Conditions over the Deep South

ifrp_0200_0500_31oct2016anim

GOES-R IFR Probability Fields, 0100-0500 UTC on 31 October 2016 (Click to enlarge)

btd_0200_0500_31oct2016anim

GOES-13 Brightness Temperature Difference Fields (3.9 µm – 10.7 µm), 0100-0500 UTC on 31 October 2016 (Click to enlarge)

Compare the two animation from 0100-0500 above, showing GOES-R IFR Probability fields  (top) and GOES-13 Brightness Temperature Difference fields (bottom) from shortly after sunset on 30 October 2016 until Midnight.  IFR Probability shows very little signal at first, and IFR conditions are rare (Jack Edwards Airport near Gulf Shores AL report IFR conditions).  IFR Probabilities increase slowly in the next 4 hours, especially in regions where IFR conditions develop.  In contrast, the trend in the Brightness Temperature Difference field is a slow decrease in areal coverage with little spatial correlation between a strong signal and IFR reports.  These animations demonstrate a strength of IFR Probabilities:  By combining satellite information with Rapid Refresh predictions of low-level saturation, a better estimate of visibility restrictions can be created.

Subsequent to 0500 UTC, in the animations shown below, IFR Probability fields expanded as IFR conditions developed over western Louisiana and southern/eastern Texas;  a strong signal develops in the brightness temperature difference field in these regions as well.  Note the lack of signal in the GOES-R IFR Probability field over Alabama and Mississippi where Brightness Temperature Difference fields show a consistent signal (and where IFR Conditions are not present).   Brightness Temperature Difference signals over those states may be related to changes in emissivity properties that occur during severe drought, as discussed here.

ifrp_0500-1215_31oct2016anim

GOES-R IFR Probability fields, 0500-1215 UTC on 31 October 2016 (Click to enlarge)

btd_0500-1215_31oct2016anim

GOES-13 Brightness Temperature Difference Fields (3.9 µm – 10.7 µm), 0500-1215 UTC on 31 October 2016

GOES-R Cloud Thickness relates future dissipation of fog to present observations of Cloud Thickness. The last pre-sunrise GOES-R Cloud Thickness field is related to dissipation time in this scatterplot. (GOES-R Cloud Thickness is not computed during twilight times surrounding sunrise and sunset)  The animation below shows the thickest clouds over south-central Texas; fog over Louisiana and coastal Texas is comparatively thin. Dissipation should occur last over interior Texas.

goes-rcloudthickness_1145-1245_31oct2016step

GOES-R Cloud thickness every half hour from 1145-1245 UTC on 31 October 2016 (click to enlarge)

IFR probabilities were noted by the Aviation Weather Center, and Dense Fog Advisories were issued along the Gulf Coast for this case.