Category Archives: GOES-16

IFR Probability indicating a Cold Front

GOES-16 IFR Probability Fields, 0607-1422 UTC on 1 June 2018 (Click to enlarge)

The animation above shows increasing amounts of IFR Probability moving southward and westward over eastern Wisconsin as a cold front with Lake-influenced air pushed inward. Ceilings lowered and visibilities reduced as the front passed, and the IFR probability field’s motion could be used to predict when the temperature change occurred. High clouds did not impede the satellite view of this event, so the brightness temperature difference field, below, also showed the stratus deck as it moved inland. Missing from the satellite-only view of this event, of course, is the information on whether the cloud is extending to the surface. Furthermore, the cloud signal vanishes from the brightness temperature difference product at sunrise, as it flips sign from positive at night to negative during the day as amounts of reflected solar 3.9 µm radiation increase.

GOES-16 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), 0607-1422 UTC on 1 June 2018 (Click to enlarge)

A Meteorogram for Milwaukee for the 24 hours ending at 1500 UTC on 1 June shows the dramatic change in ceilings, temperature and wind between 10 and 11 UTC on 1 June. A similar meteorogram for Madison (here), shows a less dramatic change at 1400 UTC on 1 June.

Meteorogram for KMKE (Mitchell International Airport, Milwaukee, WI) from 1500 UTC 31 May through 1500 UTC 1 June. Note the abrupt change in surface conditions at 1100 UTC on 1 June as the front moved through (Click to enlarge)

An animation of Low IFR Probabilities is shown below.

GOES-16 Low IFR Probability Fields, 0607-1422 UTC on 1 June 2018 (Click to enlarge)

Fog in the Canadian Maritimes

GOES-16 ABI Band 2 (0.64 µm) from 0902-1312 UTC on 9 May 2018 (Click to enlarge)

GOES-16 Visible Imagery on the morning of 9 May 2018 shows the steady erosion of fog in/around the Bay of Fundy, and along coastal Maine.  The default 5-minute temporal cadence with the CONUS GOES-16 sector allows for a precise observation for when coastal fog will clear.

The satellite view of the fog in the bay was unobstructed by high clouds.  (except to the east of Nova Scotia, where a cirrus shield is apparent in the visible animation above, and in animation below)    Thus, the GOES-16 Night Fog Brightness Temperature Difference field (10.3 µm- 3.9 µm), below, could ably capture the fog’s presence and evolution.  The animation of that product, below, shows how the signal changes at sunrise as reflected solar 3.9 µm radiation overwhelms the brightness temperature difference (driven at night by differences in emissivity at 3.9 and 10.3 µm from cloud droplets): the sign flips.  Because the fog was captured in the Night Fog Brightness Temperature Difference, it was also present in the Nighttime Microsphysics RGB Composite (here), although the color associated with fog  changes as the sun rises, and clear skies also allowed the Day Snow Fog RGB Product to show the fog during the day (here).

None of the Satellite-based products can provide information on the likelihood of fog over the ocean to the east of Nova Scotia, however, because the presence of cirrus clouds there prevents the satellite from viewing low clouds.  What products can help with that?

GOES-16 ABI Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) from 0817-1312 UTC on 9 May 2018 (Click to enlarge)

GOES-16 IFR Probability fields, below, combine together satellite and model information to determine where IFR Conditions are most likely.  Very high probabilities exist where other satellite fog detection products suggest the presence of fog/low stratus (and where surface observations confirm the presence of fog).  But there are also high probabilities over the ocean east of Nova Scotia where satellite-only fog detection fails because of the presence of high clouds;  this large signal is derived from Rapid Refresh data there that suggests low-level saturation. IFR Probability combines the strengths of both satellite data and model output to provide useful information to a forecaster.

GOES-16 IFR Probability (10.3 µm – 3.9 µm) from 0817-1322 UTC on 9 May 2018

(Thanks to Paul Ford, ECC Canada, for alerting us to this event)

Added: The GOES-16 ABI Band 3 (0.86 µm) “Veggie” Band, which has great land/sea contrast, shows the fog encroaching into the Bay of Fundy during the day on 8 May. Note in particular how the low clouds race up the west coast of Nova Scotia near sunset.

GOES-16 ABI Band 3 (0.86 µm) from 1512-2257 UTC on 8 May 2018 (Click to enlarge)

Fog over the mid-South

GOES-16 IFR Probability fields with a 10-minute time step from 0752-1422 UTC on 25 April 2018 (Click to enlarge)

Dense Fog developed over the mid-south on April 25th, and Dense Fog Advisories were issued by the National Weather Service Forecast Office in Memphis for portions of western Tennessee and northern Mississippi.  GOES-16 IFR Probability fields above, show the development of strong signal in IFR Probability over western Tennessee starting after 0900 UTC.  The satellite signal for this event was weak (see below); the sudden appearance of an IFR Probability signal at 0900 UTC suggests that the Rapid Refresh model simulation quickly changed from insufficient saturation for a strong signal to a better signal of fog when the model simulation valid at 0900 UTC was used.  When IFR Probabilities suddenly change absent a big change in satellite signal, the cause is likely a change in the Rapid Refresh model output.

Night fog Brightness temperature difference, below, shows a weak signal over river valleys of western Tennessee and northwestern Mississippi.

GOES-16 Night Fog Brightness Temperature Difference (10.3 µm – 3.9µm) 0822-1452 UTC on 25 April 2018 (Click to enlarge)

Because the signal in the brighntess temperature difference field is weak, the signal for fog in the Nighttime Microphysics RGB (which has as its green component the Night Fog Brightness Temperature Difference) is also weak. The toggle below shows the Night Fog Brightness Temperature Difference, the RGB, and the IFR Probability fields, all at 0952 UTC on 25 April.

GOES-16 Night Fog Brightness Temperature Difference (10.3 µm – 3.9µm), NIghttime Microphysics RGB and GOES-16 IFR Probability fields, all at 0952 UTC on 25 April 2018 (Click to enlarge)

IFR Conditions in the Northeast

GOES-16 IFR Probability, 1007 UTC on 20 February 2018, along with surface observations of ceilings and visibilities (Click to enlarge)

A complex set of Low Pressure systems over the eastern half of the United States brought multiple cloud layers and IFR conditions to the northeastern United States on 20 February. The image above shows the IFR Probability field at 1007 UTC. IFR Conditions are apparent from the Chesapeake Bay northeastward through southeastern Pennsylvania and New York and coastal New England, as well as over southeastern Ontario Province in Canada and the Canadian Maritimes. These are also regions where IFR Probabilities are high, generally exceeding 80%. In regions where IFR conditions are not observed (Western Pennsylvania and Ohio, for example), IFR Probabilities are generally small.

When multiple cloud decks are present, as occurred on 20 February, satellite-only detection of low clouds is a challenge, as shown with by the brightness temperature difference field (10.3 µm – 3.9 µm), called the ‘Night Fog’ difference in AWIPS, below. High and mid-level clouds (grey/black in the enhancement used) make satellite detection of low-level stratus impossible.  So, for example, stations with IFR conditions over Long Island sit under a much different enhancement in the brightness temperature difference field compared to stations with IFR conditions over southern New Jersey and southeastern Pennsylvania.

Because the Brightness Temperature Field cannot view the low clouds, the Nighttime Microphysics RGB (shown below the Brightness Temperature Difference field) similarly cannot identify all regions of low, warm clouds — typically yellow or cyan in that RGB.

Night Fog Brightness Temperature Difference field (10.3 µm – 3.9 µm) at 1007 UTC on 20 February 2018, along with surface observations of ceilings and visibilities (Click to enlarge)

NightTime Microphysics RGB at 1007 UTC on 20 February 2018, along with surface observations of ceilings and visibilities (Click to enlarge)

IFR Probability discriminates between fog and elevated stratus over Texas

GOES-16 IFR Probability field, 1127 UTC on 13 February, along with observations of ceilings and visibility. (Click to enlarge)

GOES-16 IFR Probability fields on 13 February at 1127 UTC, above, suggest a clear difference in sky conditions between northeast Texas, where IFR Probabilities are very high, and where IFR conditions are widespread, and north-central Texas, around Dallas, where IFR Probabilities are small, and where ceilings and visibilities do not match IFR Conditions.

In contrast, the Brightness Temperature Difference field, below, (and the Nighttime Microphysics Red/Green/Blue product, shown here in a toggle with the Brightness Temperature Difference field) shows little difference in signal between the region of IFR conditions over northeast Texas and non-IFR conditions over Dallas and environs.

GOES-16 views the top of the cloud, and a region of fog and a region of stratus can look very similar in the Night Fog Brightness Temperature Difference. Because IFR Probability fields fuse satellite observations of low clouds with Numerical Model Output estimates of near-surface saturation, IFR Probabilities can differentiate between regions of elevated stratus (where near-surface saturation is not suggested by the model), such as near Dallas, and regions of stratus that is obstructing visibility (where near-surface saturation is suggested by the model).

A toggle of all three fields is shown at the bottom of this post.

GOES-16 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), 1127 UTC on 13 February 2018 (Click to enlarge)

GOES-16 IFR Probabilities, Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) and NightTime Advanced Microphysics RGB, 1127 UTC on 13 February 2018 (Click to enlarge)

Advection Fog with a strong storm in the Midwest

GOES-16 IFR Probabilities, 1152 UTC on 22 January 2018, along with 1200 UTC surface observations of ceilings and visibilities (Click to enlarge)

When skies are clear, and radiation fog forms, limiting visibilities, it’s straightforward to use satellite-only products to gauge where stratus and fog might exist. Extratropical storms generate multiple cloud layers, however; when warm sector air under multiple cloud layers overruns snow-covered or frozen ground, dense advection fog can develop, and that fog is difficult to discern from satellite because it is typically overlain by higher clouds.

GOES-R IFR Probabilities, above, (and Low IFR Probabilities here) show highest probabilities in general occur in the regions where IFR conditions were observed on 22 January.  Over much of Wisconsin and Minnesota, the IFR Probability field is mostly uniform.  Such a flat field is characteristic of a region where satellite data cannot be used to judge whether low stratus is present (because high clouds are also present).  Rapid Refresh model information only is used to outline regions of low-level saturation. There is more variability to the IFR Probability field — that is, it is more pixelated — over southwest Iowa, for example, and over North Dakota.  In these regions, low stratus clouds are being observed by satellite and both satellite and model data can be used to estimate regions of significantly reduced ceilings and visibilities.

Consider the Brightness Temperature Difference shown below. The 10.3 µm – 3.9 µm product is typically used to identify stratus and radiation fog, and it does detect those low clouds over North Dakota, and over Kansas, Missouri and southern Iowa, and over Ontario.  However, the dense clouds associated with the storm over much of Minnesota and Wisconsin meant that this brightness temperature difference field, and also the NightTime Microphysics Red Green Blue Product (which is sometimes used to detect fog), could not ‘see’ the fog over the upper midwest.

Know the limitations, strengths and weaknesses of your products as you use them!  On 22 January, High Clouds underscored limitations in the Brightness Temperature Difference product, and in the NightTime Microphysics product that relies on the Brightness Tempearature Difference product for fog detection.  That limitation meant the product was not useful in identifying IFR conditions in parts of the Upper Midwest.

GOES-16 “Night Fog” Brightness Temperature Difference (10.3 µm – 3.9 µm) at 1152 UTC on 22 January 2018. Surface reports of ceilings and visibilities at 1200 UTC are also plotted (Click to enlarge)

Dense Fog Advisories over the Plains

Dense Fog Advisories were issued over parts of the central and northern Plains states on Friday January 5. For example, from the North Platte Office (similar warnings were issued by Billings, Rapid City and Bismark offices):

URGENT – WEATHER MESSAGE
National Weather Service North Platte NE
634 AM CST Fri Jan 5 2018

…Areas of dense fog likely this morning…

.Areas of fog reducing visibilities below one quarter mile at
times will be likely from parts of southwest into the central
Nebraska Sandhills this morning. With the fog occurring where
temperatures are below freezing, some slick spots may develop on
area roads and sidewalks as well.

NEZ025-026-037-038-059-071-051800-
/O.NEW.KLBF.FG.Y.0001.180105T1234Z-180105T1800Z/
Thomas-Blaine-Logan-Custer-Lincoln-Frontier-
Including the cities of Thedford, Halsey, Dunning, Purdum,
Brewster, Stapleton, Broken Bow, North Platte, Curtis, Eustis,
and Maywood
634 AM CST Fri Jan 5 2018

…DENSE FOG ADVISORY IN EFFECT UNTIL NOON CST TODAY…

The National Weather Service in North Platte has issued a Dense
Fog Advisory, which is in effect until noon CST today.

* Visibilities…as low as one quarter mile or less at times.

* Timing…Through the morning hours with visibilities improving
after noon CST.

* Impacts…Hazardous driving conditions due to low visibility.
Fog may freeze on area roads and walkways as well.

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 headlights, and leave plenty of distance ahead of you.

&&

$$

JWS

GOES-16 IFR Probability fields captured the development of these regions of dense fog. The animation from 0400-1200 UTC on 5 January is below. Highest values of IFR Probability are consistent in the areas where IFR Conditions are developing and where Dense Fog Advisories were issued.

GOES-16 IFR Probability, 0402 – 1207 UTC on 5 January 2018 (Click to animate)

Note that IFR Probability fields are fairly high over Iowa and the eastern Dakotas, regions where mid-level stratus was widespread but where IFR observations did not occur. On this day, Low IFR Probability fields better screened out this region of mid-level stratus. The toggle below compares IFR Probability and Low IFR Probability on 0957 UTC. The region where dense fog advisories were issued shows high values in both fields. The stratus deck over Iowa and the eastern Dakotas shows much smaller values of Low IFR Probability.

GOES-16 also has a ‘Fog Product’ brightness temperature difference (10.3 – 3.9) that has historically been used to detect low clouds. However, when cirrus clouds are present, as on 5 January, the efficacy of this product in fog detection is affected. Although fog and stratus detection is identifiable underneath the moving cirrus (the same is true in the Advanced NightTime Microphysics RGB product below), identifying the low cloud as stratus or fog from satellite data is a challenge because a consistent color married to IFR Probability does not exist.

GOES-16 ‘Fog Product’ Brightness Temperature Difference (10.3 µm – 3.9 µm), 0402 – 1207 UTC, 5 January 2017 (Click to animate)

GOES-16 Advanced Nighttime Microphysics RGB, 0402-1207 UTC on 5 January 2018 (Click to animate)

GOES-16 IFR Probability fields maintain a consistent look from night to day. Both the (10.3 µm – 3.9 µm) Brightness Temperature Difference field and the Advanced Nighttime Microphysics RGB (that uses the ‘Fog Product’ BTD) will change because the increase in reflected solar radiation at 3.9 µm will change the sign of the Brightness Temperature Difference field. There is a Daytime Day/Snow/Fog RGB Product in AWIPS, and the toggle below from 1612 UTC on 5 January compares IFR Probability and the Day/Snow/Fog RGB. As with the nighttime products, the presence of high (or mid-level) clouds makes it difficult to use the RGB alone to identify regions of fog/low stratus. In contrast, the IFR Probability field continues to correctly identify where the obstructions to visibility exist.

Dense Fog over the Deep South

GOES-16 IFR Probability fields, 1312 UTC on 18 December 2017 (Click to enlarge). Ceilings and visibilities are also plotted.

Dense Fog was widespread across the south on Monday morning, 18 December 2017 (See the screen capture below from this site at 1319 UTC).  The GOES-16 IFR Probability field, above, highlights the regions of IFR and near-IFR conditions very well. It has a flat character over much of central Mississippi and Alabama.  These are regions where multiple cloud decks are preventing the satellite from viewing the near-surface clouds, and where Rapid Refresh data are being used as the sole predictor for the probability of IFR conditions.  In contrast, the IFR Probability field over much of Tennessee and Arkansas (for example) has a pixelated look to it — there are small variations over very small distances:  over these two states, higher clouds are not preventing the satellite from viewing near-surface clouds, and satellite data can also be used as a predictor in the IFR Probability fields (See the 10.3 µm – 3.9 µm Brightness Temperature difference field below).

Screen Capture from http://www.weather.gov at 1319 UTC on 18 December 2017 (Click to enlarge). Grey regions are under Dense Fog Advisories.

When high clouds are present, fog detection techniques that rely solely on satellite data struggle to detect low clouds.  Compare the above field, for example, to the 10.3 µm – 3.9 µm Brightness Temperature Difference field (sometimes called the ‘Fog Product’).  In the enhancement used (the default enhancement in AWIPS), fog is depicted as blue (a positive value in the brightness temperature difference) and cirrus/high clouds in black.  There is little signal of Fog over a region where Dense Fog advisories have been issued. Similarly, the Advanced Nighttime Microphysics RGB, below, that relies on the 10.3 µm – 3.9 µm to highlight low clouds that might be fog, also is not indicating fog (a light cream/cyan color, typically) over much of the Deep South.  When cirrus clouds are present, its use, like that of the Fog Brightness Temperature Difference, is of dubious value.

The last figure, at the bottom, toggles between all three fields at 1312 UTC.

GOES-16 Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) field, 1312 UTC on 18 December 2017  (Click to enlarge)

Advanced Nighttime Microphysics RGB, 1312 UTC on 18 December 2017  (Click to enlarge)

GOES-16 IFR Probability, GOES-16 ‘Fog’ Brightness Temperature Difference (10.3 µm – 3.9 µm), and Advanced Nighttime Microphysics RGB, all at 1312 UTC on 18 December 2017 (Click to enlarge)

Dense Fog over Idaho

GOES-16 IFR Probability fields, 0502-1302 UTC on 15 December 2017 (Click to enlarge)

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

GOES-16 is now in the operational GOES-East position (but not, yet, technically operational) and GOES-16 data started flowing shortly after 1500 UTC on Thursday 14 December. GOES-16 produces excellent imagery over the western United States despite the satellite’s station at 75.2 West Longitude. The animation above shows GOES-16 IFR Probability fields over Idaho, with large values over the Snake River; High Pressure over the region has capped moisture (and pollutants) in the valley, and reduced visibilities are a result. (Click here for the Boise Sounding from 0000 UTC on 15 December from this site) The Pocatello Idaho Forecast Office of the NWS issued (at bottom) Dense Fog Advisories that were valid in the morning of 15 December 2017.

The excellent temporal resolution allows for close monitoring of the eastern edge of the region of fog, expanding eastward from the Snake River Valley into Wyoming and Montana.

The animation above shows consistent GOES-16 IFR Probabilities over the Snake River, and observations of low ceilings and reduced visibilities.  Note that over the eastern part of the Valley, from Pocatello to Idaho Falls and Rexburg, the character of the IFR Probability field at times loses all pixelation.  During this time (around 1000 UTC), model data (in the form of low-level saturation in the Rapid Refresh Model) are contributing to the IFR Probability Field, but satellite data are not because of high-level cirrus.  The animation, below, of the Nighttime Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), confirms the presence of cirrus (they appear grey/black in the color enhancement).  It also suggests why that field alone rather than a fused field such as GOES-R IFR Probability can struggle to detect fog in regions of cirrus.

GOES-16 Brightness Temperature Difference Field (10.3 µm – 3.9 µm), 0502-1302 UTC on 15 December 2017 (Click to animate)

Products that use only satellite data, such as the Brightness Temperature Difference field, above, or the Advanced Nighttime Microphysics RGB Product, below, that uses the (10.3 µm – 3.9 µm) Brightness Temperature Difference field as the ‘Green’ component, will always struggle to detect fog in regions of cirrus. Of course, the superb temporal resolution of GOES-16 mitigates that effect, as in this case; it’s obvious in this animation what is going on: a band of cirrus is moving over the fog, but it not likely affecting it.  A single snapshot of the scene, however, might not impart the true character of surface conditions.

Advanced NIghttime Microphysics RGB Composite, 0502-1302 UTC on 15 December 2017 (Click to enlarge)

Screencapture of WFO PIH (Pocatello Idaho) Website from 1320 UTC on 15 December 2017 (Click to enlarge)

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)