Category Archives: Pacific Northwest

Fog over the Pacific Northwest: Where is it?

GOES-17 imagery in this blog post is made from GOES-17 Data that are preliminary and non-operational!

Night Time Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) from GOES-16 and (preliminary, non-operational) GOES-17, 1202 UTC on 3 December 2018 (Click to enlarge)

The toggle above shows GOES-16 and GOES-17 Night Fog Brightness Temperature difference fields over the Pacific Northwest shortly after 1200 UTC on 3 December 2018.  The Pacific NW is a lot farther from the sub-satellite point (nadir) of GOES-16 (75.2 West Longitude) than from the sub-satellite point (nadir) of GOES-17 (at 137.2 W Longitude).  Thus, the GOES-16 view is has inferior spatial resolution.  There are also different parallax shifts for clouds between the two views.  The scene includes plenty of stratus, based on the observations, and isolated pockets of IFR conditions:  Spokane WA, Stampede Pass, WA, Pendleton OR, Medford OR, Salem OR.  It’s difficult to tell at a glance from the Brightness Temperature Difference field where the lowest ceilings and poorest visibilities are — because the satellite sees the top of the cloud, and it’s difficult to infer cloud base properties from infrared imagery of the cloud top.

The Advanced Nighttime Microphysics RGB can also be used to detect low ceilings, because its green component is the Night Fog Brightness Temperature Difference as shown above.  The toggle below compares the GOES-16 and GOES-17 RGBs.  Again, it is difficult to pinpoint at a glance where the IFR conditions are occurring in this product.

There are subtle differences in the colors of the RGB from the two satellites.  These are related to the distance from the sub-satellite point.  Limb cooling will cause the brightness temperatures from the GOES-16 Clean Window to be slightly cooler than the GOES-17 values, and that will affect the color:  The Clean Window is the Blue component of the RGB.  In addition, the Split Window Difference values will be slightly different because of the different amounts of limb cooling in 12.3 µm and 10.3 µm brightness temperatures.  GOES-17 data also includes striping that is being addressed with ongoing calibration work with the satellite.

Advanced Nighttime Microphysics RGB from GOES-16 and GOES-17 at 1202 UTC on 3 December 2018 (Click to enlarge)

The toggle below shows, (from GOES-16 data) the 10.3 µm – 3.9 µm Brightness Temperature Difference, the Nighttime Microphysics RGB, and the IFR Probability fields at 1202 UTC. IFR Probability fields include information about low-level saturation from the Rapid Refresh model, and that information allows the product to screen out regions of mid-level stratus; thus, the region of IFR conditions is better captured.  There are three main regions:  eastern WA southwestward to Pendleton OR, Seattle southward into Oregon, and the peaks of central Washington.

GOES-16 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), Nighttime Microphysics RGB and IFR Probability, 1202 UTC on 3 December 2018 (Click to enlarge)

Fog under multiple cloud layers

GOES-16 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), 1137 – 1452 UTC on 31 October 2018 (Click to animate)

Consider the imagery above: The Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) product can be used to highlight regions of low clouds (cloud made up of water droplets) because those water droplets do not emit 3.9 µm radiation as a blackbody (but do emit 10.3 µm radiation nearly as a blackbody), and the conversion of sensed radiance to brightness temperature assumes blackbody emissions. Thus, the 10.3 µm brightness temperature is warmer than at 3.9 µm. In the enhancement used, low stratus clouds are shades of cyan. Is there fog/low stratus along the coast of the Pacific Northwest? How far inland does it penetrate. It is impossible in this case (and many similar cases) to tell from satellite imagery alone because multiple cloud layers associated with a storm moving onshore prevent the satellite from seeing low clouds. The animation shows the Brightness Temperature Difference field along with surface reports of visibility and ceilings.  IFR and near-IFR conditions are widespread, but there is little correlation between their location and the satellite-only signal.

GOES-16 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), 1137 – 1452 UTC on 31 October 2018, along with surface reports of ceilings (AGL) and visibility (Click to animate)

GOES-R IFR Probability fields fuse together satellite information and model data to provide a better estimate of where IFR conditions might be occurring. The animation below, for the same times as above, shows a high likelihood of IFR conditions (as observed) over much of the eastern third of Washington State. The satellite doesn’t give information about the near-surface conditions in this case, but the Rapid Refresh data strongly suggests low-level saturation, so IFR probabilities are high. The field also correctly shows small likelihood of IFR probailities over coastal southern Oregon and northern California. The Rapid Refresh data used have 13-km resolution, however; fog at scales smaller than that may be present — in small valleys for example.

GOES-16 IFR Probabilities, 1137 – 1452 UTC on 31 October 2018 (Click to animate)

Detecting Fog under a Pall of Smoke in the Pacific Northwest

HRRR forecast of Vertically-Integrated Smoke over the Pacific Northwest (for more information see text), forecast valid at 1200 UTC on 30 July 2018 (Click to enlarge)

When smoke covers a geographic region, visible detection of low-level fog is difficult because smoke can scatter or obscure the signal from the low-level clouds.  The image above shows a Vertically Integrated Smoke Forecast from a High-Resolution Rapid Refresh Model simulation in Real Earth (link). Thick smoke was predicted to occur over the coast of Oregon.

The animation below steps through the GOES-R IFR Probability, and then the ‘Blue Band’ (0.47 µm), the ‘Red Band’) (0.64 µm), the ABI channel with the highest spatial resolution, the ‘Veggie Band’ (0.86 µm) and the ‘Snow/Ice Band’ (1.61 µm). Two things of note: Because of the low sun angle, and the enhanced forward-scattering properties of smoke at low sun angle, it is very hard to detect fog through the smoke in the visible wavelengths near Sunrise. As the wavelength of the observation increases, scattering is less of an issue. In addition, smoke is more transparent to longer wavelength radiation. Thus, the cloud edges become more apparent under the smoke in the 0.86 µm and especially the 1.61 µm imagery compared to the visible.

GOES-16 IFR Probability, and GOES-16 Single Bands (Band 1, 0.47 µm, Band 2, 0.64 µm, Band 3, 0.86 µm and Band 5, 1.61 µm) at 1342 UTC on 30 July 2018, along with surface observations of Ceilings, Visibility, and Visibility Restrictions at 1400 UTC. (Click to enlarge)

GOES-16 IFR Probability can indicate the regions of fog and corresponding restrictions in visibility because it relies on longer wavelength observations from GOES-16 (3.9 µm and 10.3 µm, principally) and information about low-level saturation from the Rapid Refresh model.  Smoke is mostly transparent to radiation in the infrared unless it becomes extraordinarily thick  (indeed, that is one reason why smoke is difficult to detect at night);  thus, the brightness temperature difference between the shortwave (3.9 µm)  and longwave (10.3 µm) infrared channels on GOES-16’s ABI can highlight cloud tops made up of water droplets that occur underneath elevated smoke.

As the Sun gets higher in the sky, fog edges beneath the smoke become more apparent because forward scattering decreases.  The animation below of the visible confirms this. In contrast, the fog edge in the IFR Probability is well-represented during the entire animation (although the horizontal resolution of the infrared channels on GOES-16 (at the sub-satellite point) is only two kilometers vs. 1/2-km for the Red Visible).

Note that IFR conditions are also occurring during this animation due to smoke over southwest Oregon.  GOES-R IFR probability detects only cloud-forced IFR conditions, but not IFR conditions because of thick smoke only.  Again, this is because smoke detection in the infrared is a challenge for ABI Channels and Rapid Refresh Model output does not as yet predict visibility restrictions due to smoke.

GOES-16 ABI ‘Red Visible’ Imagery (0.64 µm), 1342 – 1557 UTC on 30 July 2018, along with surface observations of Ceilings, Visibility, and Visibility Restrictions (Click to enlarge)

GOES-16 IFR Probability, 1342 – 1557 UTC on 30 July 2018, along with surface observations of Ceilings, Visibility, and Visibility Restrictions (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)

IFR Conditions in Pennsylvania and Oregon

GOES-16 Brightness Temperature Difference (10.3 µm – 3.9 µm) at 0912 UTC on 2 October 2017 over the Mid-Atlantic States (click to enlarge)

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

The images above show the GOES-16 Brightness Temperature Difference at the same time at two places over the United States: The mid-Atlantic States (above) and Oregon and surrounding States (below).  The ‘Fog’ Product, as this Brightness Temperature Difference is commonly called, in reality identifies only clouds that are made up of water droplets — that is, stratus.  A cloud made up of water droplets emits 10.3 µm radiation nearly as a blackbody does. Thus, the computation of Brightness Temperature — which computation assumes a blackbody emission — results is a temperature close to that which might be observed.  In contrast, those water droplets do not emit 3.9 µm radiation as a blackbody would.  Thus, the amount of radiation detected by the satellite is smaller than would be detected if blackbody emissions were occurring, and the computation of blackbody temperature therefore yields a colder temperature, and the brightness temperature difference field, above, will show clouds made up of water droplets as positive, or cyan in the enhancement above.

The River Valleys of the northeast show a very strong signal that suggests Radiation Fog is developing over the relatively warm waters in the Valleys.  The Delaware, Hudson, Mohawk, Connecticut, Susquehanna, Allegheny, Monongahela, and others — all show a signature that one would associate with fog.  A signal is also apparent from southern New Jersey southwestward through the Piedmont of North Carolina.  Would you expect there to be fog there as well, given the signal?

The State of Oregon at the same time shows a very strong signal in the ‘Fog’ Product.  A clue that this might be only stratus, and not visibility-restricting fog, lies in the structure of the clouds — they do not seem to be constrained by topographic features as is common with fog.

GOES-16 Brightness Temperature Difference (10.3 µm – 3.9 µm) at 0912 UTC on 2 October 2017 over Oregon and adjacent States (click to enlarge)

GOES-R IFR Probabilities are computed using Legacy GOES (GOES-13 and GOES-15) and Rapid Refresh model information; Preliminary IFR Probability fields computed with GOES-16 data are available here.  These GOES-16 fields should be available via LDM Request when GOES-16 becomes operational as GOES-East.

GOES-R IFR Probability Fields use both the Brightness Temperature Difference field (10.7 µm – 3.9 µm) from heritage GOES instruments and information about low-level saturation from Rapid Refresh Model output.  The horizontal resolution on GOES-13 and GOES-15 is coarser than on GOES-16 (4 kilometers at the sub-satellite point vs. 2 kilometers), so small river valleys will not be resolved.  (It is also difficult for the Rapid Refresh model to resolve small valleys).

GOES-R IFR Probability fields at 0915 UTC, along with 0900 UTC surface observations of ceilings and visibility (Click to enlarge)

The IFR Probability Fields, above, show some signal over the river valleys of the northeast; that signal is mostly satellite-based, but the poor resolution of GOES-13 means that fog/stratus in the river valleys is not well-resolved. Still, a seasoned forecaster could likely interpret the small signals that are developing to mean fog is in the Valleys.  (And restrictions to ceilings and visibilities are certainly reported in the river valleys of the Mid-Atlantic and Northeast)   IFR Probabilities are also noticeable over southeast Virginia, although widespread surface observations showing IFR Conditions are not present.  (Such observations are somewhat more common near sunrise, at 1130 UTC).

IFR Probabilities are much less widespread over Oregon, with most of the signal over western Oregon related to the topography.  In this example, IFR Probabilities are ably screening out regions where elevated stratus is creating a strong signal for the satellite in the Brightness Temperature Difference field.

What GOES-16 Resolution will bring to IFR Probability

GOES-16 Brightness Temperature Difference field (10.3 µm – 3.9 µm) at 1247 UTC on 5 July 2017 (Click to enlarge)

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

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 continue to be created using legacy GOES (GOES-13 and GOES-15) data. This is slated to continue through late 2017. The toggle above, over Oregon, hints at how the change in resolution in GOES-16, even far from the sub-satellite point, will likely improve GOES-R IFR Probability performance in regions where topography can constrain low clouds and fog.  The GOES-16 Brightness Temperature Difference field, above, is color enhanced so that positive values (that is, where the brightness temperature at 10.3 µm is warmer than the 3.9 µm brightness temperature, which regions indicate cloud tops composed of water droplets, i.e., stratus) are whitish — and the data shows stratus/fog along the Oregon Coast, with fingers of fog advancing up small valleys.  The image below shows the GOES-R IFR Probability field for the same time (Click here for a toggle).

GOES-R IFR Probability fields show strong probabilities where the Brightness Temperature Difference field above is indicating low clouds.  This is not surprising as the morning fog on this date was not overlain by higher clouds.  However, the resolution inherent in the legacy GOES (inferior resolution compared to GOES-16), shows up plainly as a blocky field.  When GOES-R IFR Probability fields are computed using GOES-16 data, the IFR Probability field resolution will match the GOES-16 resolution.  (Click here for a aviationweather.gov observation of IFR / Low IFR conditions on the morning of 5 July).

GOES-R IFR Probability field computed from GOES-15 data at 1245 UTC on 5 July 2017 (Click to enlarge)

A similar set of figures for California at the same time is below.  The toggle is here, and the aviationweather.gov screen capture is here.

GOES-16 Brightness Temperature Difference field (10.3 µm – 3.9 µm) at 1247 UTC on 5 July 2017 (Click to enlarge)

GOES-R IFR Probability field computed from GOES-15 data at 1245 UTC on 5 July 2017 (Click to enlarge)

 

IFR Probability and Low IFR Probability in the Pacific Northwest

GOES-R IFR Probability fields, hourly from 0300 through 1500 UTC on 4 May 2017 (Click to enlarge)

GOES-R Low IFR Probability fields, hourly from 0300 through 1500 UTC on 4 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.

Dense fog with IFR and Low IFR Conditions occurred along the Oregon and Washington Coasts early on 4 May 2017. The animations above show the evolution of IFR Probability and Low IFR Probability. Note that IFR Conditions/Low IFR Conditions mostly occurred where Probabilities were high, with a few exceptions (KSMP, Stampede Pass, WA; KKLS, Kelso WA at 1400 UTC). Both IFR and Low IFR Probabilities show a general areal increased between 0800 and 0900; this can be traced to a big increase in the brightness temperature difference that occurred between 0845 and 0900 UTC (shown here) that is likely due to stray light intruding into the satellite detectors. (Brightness Temperature Difference values decreased after 0900 UTC — note that the Brightness Temperature Difference enhancement has color starting when ‘counts’ in the image reach -6).

Low IFR Probabilities do a particularly good job above of outlining the regions of visibility and ceiling restrictions along the coasts of Oregon and of Puget Sound.  Note also that a strip of missing satellite data exists at 1100 UTC over northern Washington.  When satellite data are missing completely, IFR Probabilities are not computed.

A difficulty in using Brightness Temperature Difference fields is shown below. The 1300 and 1400 UTC Brightness Temperature Difference fields show an apparent decrease in low clouds detected as the sun rises (in reality, the amount of reflected 3.9 radiation is increasing as the Sun rises). Fog persists through sunrise as shown in the observations; IFR Probabilities (and Low IFR Probabilities) maintain a signal throughout sunrise.

GOES-15 Brightness Temperature Difference (3.9 µm – 10.7 µm) at 1300 and 1400 UTC on 4 May 2017 followed by GOES-R IFR Probability fields at 1300 and 1400 UTC on 4 May 2017 (Click to enlarge)

Dense Fog in Oregon

GOES-R IFR Probabilities computed with GOES-15 and Rapid Refresh Data, hourly from 0300 through 1400 UTC on 21 December 2016 (Click to enlarge)

Dense Fog developed in the Willamette Valley of western Oregon during the early morning hours of 21 December 2016.  How did GOES-R IFR Probability fields and GOES-15 Brightness Temperature Difference (3.9 µm – 10.7 µm) Fields diagnose this event that led to the issuance of Dense Fog Advisories? The hourly GOES-R IFR Probability animation, above, shows increasing probabilities in the Willamette Valley, starting around Eugene (KEUG) and spreading northward until high probabilities cover the valley by 1400 UTC. IFR Conditions are first reported near Eugene, then through the entire valley by 1400 UTC. Widespread high IFR Probability values are not present elsewhere over Oregon (although they do exist over Washington State, where IFR conditions were also observed).

The Brightness Temperature Difference field (3.9 µm – 10.7 µm), below, shows a different distribution. Early in the animation a strong signal is apparent over much of northern Oregon, and also over the Pacific Ocean. Rapid Refresh output on low-level saturation is used in the GOES-R IFR probability algorithm to screen out regions where stratus that is detected by the satellite likely is not extending down to the surface — over the ocean, for example (coastal sites do not show IFR Conditions), or over much of eastern Oregon/Washington.   Brightness Temperature Difference fields do eventually highlight the presence of fog in the Willamette Valley, but considerable regions outside the valley have a strong return and no indication of IFR conditions.

GOES-15 Brightness Temperature Difference (3.9 µm – 10.7 µm) fields, 0300-1300 on 21 December 2016 (Click to enlarge)

GOES-R IFR Probability fields will frequently (and correctly) screen out regions of strong returns in the Brightness Temperature Difference fields that do not correspond to surface obscuration of visibility and/or low ceilings.

It is possible to alter the Brightness Temperature Difference Colormap, as below (animation courtesy Mike Stavish, SOO at Medford) to better highlight regions of fog in this case.  Note in this enhancement the cirrus clouds appear white, rather than dark, as well.

GOES-15 Brightness Temperature Difference  (3.9 µm – 10.7 µm) Fields, hourly from 0800 to 1400 UTC on 21 December 2016 (Click to enlarge)

The toggle below shows two color enhancements at 1200 UTC: the default version with many orange pixels, and an altered version that shows fewer pixels, mostly in regions where fog is present. A similar toggle for 0400 UTC is here.

Brightness Temperature Difference (3.9 µm – 10.7 µm) fields at 1200 UTC with two different enhancements. (Click to enlarge)

The Challenge of Satellite Fog Detection at Very Small Scales

weather-gov-screencapture_1400utc_10nove2016

Hazards as depicted by http://weather.gov front page at 1400 UTC on 10 November 2016 (Click to enlarge)

Isolated regions of dense fog developed over eastern Oregon early in the morning on 10 November 2016, and one county — around Baker City — was placed in a Dense Fog advisory (Counties in the Willamette Valley of western Oregon, and near Glacier Park in Montana were placed under Dense Fog Advisories a bit later in the morning on 10 November). Click here to see a 1400 UTC mapping of IFR/LIFR conditions from the Aviation Weather Center.

URGENT – WEATHER MESSAGE
NATIONAL WEATHER SERVICE BOISE ID
600 AM MST THU NOV 10 2016

ORZ062-101800-
/O.NEW.KBOI.FG.Y.0012.161110T1300Z-161110T1800Z/
BAKER COUNTY-
500 AM PST THU NOV 10 2016

…DENSE FOG ADVISORY IN EFFECT UNTIL 10 AM PST THIS MORNING…

THE NATIONAL WEATHER SERVICE IN BOISE HAS ISSUED A DENSE FOG
ADVISORY…WHICH IS IN EFFECT UNTIL 10 AM PST THIS MORNING.

* VISIBILITY…ONE QUARTER MILE OR LESS.

* IMPACTS…TRAVEL HAZARD DUE TO POOR VISIBILITY…ESPECIALLY
ALONG INTERSTATE 84 BETWEEN BAKER CITY AND NORTH POWDER

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.

&&

$$

What kind of Fog-detection products are available to assist a forecaster in seeing at a glance that fog is developing? How useful are they for small-scale features such as that in Baker County Oregon?

Brightness Temperature Difference Fields (3.9 µm – 10.7 µm) have historically been used to detect fog; the difference field keys on the Emissivity Differences that exist in water-based cloud droplets: they do not emit 3.9 µm radiation as a blackbody, but do emit 10.7 µm radiation more nearly as a blackbody, so computed brightness temperatures are different: cooler at 3.9 µm than at 10.7 µm. The Brightness Temperature Difference fields for 0900 and 1200 UTC are shown below (Note the seam — GOES-13 data are used east of the seam, GOES-15 data are used to the west). There is no distinct signal over Baker County, nor any pattern that can really help identify regions of fog. Cirrus is present over western Oregon (depicted as dark grey or black in this enhancement); satellite-only detection of low fog is not possible if cirrus prevents a view of the surface.

goes15btd_10nov_0900_1200toggle

GOES Brightness Temperature Difference Fields (3.9 µm – 10.7 µm) at 0900 and 1200 UTC on 10 November 2016 (Click to enlarge)

For a small-scale event, the nominal 4-km pixel size on GOES-15 and GOES-13 (a size that is closer to 6-7 km over Oregon because of the distance from the sub-satellite point) may prevent satellite detection of developing fog. The toggle below shows Brightness Temperature Difference fields at 0928 UTC from MODIS on Aqua, as well as the GOES-R IFR Probability fields computed using the MODIS data.  As with GOES data, the presence of cirrus in the Brightness Temperature Difference field is obvious and shown by a black enhancement.  Little signal is present over Baker County.  (There is a strong signal, however, in the valleys of northwest Montana and northern Idaho — compare this to the GOES-based brightness temperature difference above).

Note:  MODIS resolution is 1-km;  data from the Advanced Baseline Imager (ABI) on GOES-R will have nominal 2-km resolution at the sub-satellite point.

modis_btd_ifr_10nov_0928toggle

MODIS Brightness Temperature Difference fields (3.7 µm – 11 µm) and MODIS-based GOES-R IFR Probability, 0928 UTC on 10 November 2016 (Click to enlarge)

What does the GOES-based GOES-R IFR Probability field show during the early morning hours of 10 November? The animation below, from 0800-1200 UTC, shows some returns in/around Baker County. It would have been difficult to use this product alone to diagnose this fog feature however. (It did do a better job of diagnosing the presence of fog over northwest Montana and western Oregon where Advisories were later issued).

goesr_ifr_10nov_0800_1200anim

GOES-R IFR Probability fields, hourly from 0800 – 1200 UTC on 10 November 2016 (Click to enlarge)

Small-scale Fog Event near Puget Sound

IFRProbability_9Feb_11_22UTCanim

GOES-R IFR Probabilities computed with GOES-15 and Rapid Refresh Data, 1100-2200 UTC on 9 February 2016 (Click to enlarge)

GOES-R IFR probabilities on Tuesday 9 February captured the development of a small-scale fog event in/around the southern part of Puget Sound in Washington State. The animation above shows high IFR Probabilities developing shortly before sunrise and persisting through most of the day in a region including Shelton, Olympia, Tacoma and Seattle.

MODIS visible data, below, from the Terra Satellite overpass shortly after 1800 UTC, below, shows the fogbank over the most of Puget Sound, extending inland only over the southern part of the sound.

MODISVIS_1822

MODIS Visible Imagery (0.65 µm), 1822 UTC on 9 February (Click to enlarge)

Suomi NPP viewed Puget Sound on two consecutive overpasses on 9 February, and visible imagery from those passes, just before 2000 UTC and near 2130 UTC, are shown below.  Fog Dissipation is apparent in the later image, which is consistent with the animation of IFR Probability at the top of this post, which animation shows IFR Probabilities declining in value after 2100 UTC.

SNPPVIS_1953_2122step

Suomi NPP Visible Imagery (0.64 µm), 1953 and 2122 UTC on 9 February (Click to enlarge)