Category Archives: Suomi/NPP

IFR Probabilities during a Winter Storm

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GOES-R IFR Probabilities computed from GOES-East and Rapid Refresh model output, from 0100 through 1400 UTC on March 25 2013

A late winter storm moving through the mid-Altantic states was responsible for an episode of reduced visibilities.  The loop above shows two areas of reduced visibilities initially — one over the Piedmont of Georgia, the Carolinas and Virginia, and one over the Ohio River Valley.  Visibilities decrease as the higher IFR probabilities move in, and, conversely, increase as the higher probabilities move out.  IFR Probabilities over southern Ohio, for example, have a character that suggests the probabilities have been computed chiefly with model data.  Probabilities are somewhat reduced, and the fields are not pixelated (as they are over the Carolina Piedmont, for example).

GOES-R IFR Probabilities computed from GOES-East, Brightness Temperature Difference fields from GOES-East (10.7 µm – 3.9 µm) and from Suomi/NPP (10.8 µm- 3.74 µm) around 0700 UTC on 25 March 2013

The animation of the ~0700 UTC IFR Probability and brightness temperature difference field from both GOES-East and from the polar-orbiting Suomi/NPP, above, shows another strength of the IFR Probability product:  It screens out regions where high stratus give a signal.  The top of a stratus deck and the top of a fog deck may have a very similar brightness temperature difference signal.  By fusing the satellite data with a product that includes surface information (such as output from the Rapid Refresh Model), regions with elevated stratus, which clouds do not significantly impact aviation operations, can be removed from the signal.  Only regions with actual surface observation restrictions are highlighted in the IFR probability signal above.

Cold frontal passage in Oregon

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GOES-R IFR Probabilities (Upper Left), GOES-West Brightness Temperature Difference (10.7 µm – 3.9 µm) (Upper Right), Topography (Lower Left), GOES-West Water Vapor Imagery (6.7 µm) (Lower Left), hourly from 0400 through 1700 UTC 20 March 2013.

The animation above of the Fog/Low Stratus and Brightness Temperature difference highlights the difficulty that the traditional brightness temperature difference product encounters when multiple cloud layers are present, as you might expect to be present given the water vapor imagery.  At the beginning of the animation, highest IFR probabilities exist over the elevated terrain that surrounds the Willamette Valley in Oregon.  There were also high probabilities off shore.  As the frontal region moves onshore, IFR probabilities increase on shore.   Note also how the GOES-R IFR Probability field is a more coherent one whereas the traditional brightness temperature difference field from GOES contains many separate areas of return that make it harder to see the big picture.  The brightness temperature difference also suffers from stray light contamination at 1000 UTC — but that contamination does not propagate into the GOES-R IFR probability field.
GOES-R IFR Probabilities computed from GOES-West (Upper Left), GOES-West Brightness Temperature Difference (10.7 µm – 3.9 µm) (Upper Right), Topography (Lower Left), Toggle between Suomi/NPP Brightness Temperature Difference (10.8 µm – 3.74 µm) and Day/Night Band, all imagery near 1000 UTC on 20 March 2013

The imagery above shows how straylight contamination in the shortwave IR (3.9 µm) can influence the brightness temperature difference.  The GOES imagery shows the effects (just at this 1000 UTC image, which is also included in the animation above), but that ‘contamination’ does not propagate strongly into the GOES-R IFR Probability.  Note also that the Suomi/NPP Brightness Temperature Difference shows none of the stray light contamination.  Lunar illumination  allows the nighttime visualization of the clouds off the west coast of the US.  As this frontal band moves over Oregon, reduced visibilities result, but only the GOES-R IFR probabilities accurately capture the location of the frontal band because of the multiple cloud layers that exist.

Resolution Issues over the Pacific Northwest

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GOES-R IFR Probabilities computed from GOES-West (Upper Left), GOES-E/W Brightness Temperature Difference (10.7 µm – 3.9µm) (Upper Right), GOES-R Cloud Thickness (Lower Left), Suomi/NPP VIIRS Brightness Temperature Difference  (Lower Right)
As on top, but with MODIS Brightness Temperature Difference (11 µm – 3.7 µm) in the bottom right.

The imagery above underscores the power of higher resolution on fog detection.  The images on the right side of the images are brightness temperature difference fields, the heritage method for detecting fog and low stratus.  The GOES field (top right) actually includes data from GOES-East (eastern Washington and points east — a faint seam is discernible in the image) and GOES-West (western Washington).  Pixel size over Washington is large — 6 or 8 kilometers (vs. 4 kilometers at the subsatellite point).  In contrast, Suomi/NPP VIIRS data and MODIS data (bottom right) has a resolution of 1 km.  The brightness temperature difference from MODIS and VIIRS more easily resolves the fine-scale structure of the topographically influenced or topographically constrained fog and low stratus.  The brightness temperature difference field from GOES is one of the predictors used to generate the IFR Probabilities shown in the upper right.  When poor resolution smears out the horizontal domain of the fog and low stratus in the brightness temperature difference field, you might expect a similar effect on the IFR probabilities.

As above, but with MODIS-based GOES-R IFR Probabilities in the lower right

 MODIS data can be used to compute IFR probabilities.  Compare the lower right and upper left figures.  High MODIS IFR Probabilities are far more restricted to regions where IFR conditions are observed.  In contrast, GOES-based IFR probabilities seem to leak into regions where IFR conditions are not reported.

The higher resolution MODIS-based IFR Probabilities (and coming soon, Suomi/NPP-based IFR probabilities) nicely complement the higher temporal resolution of the GOES imagery.  Ideally, use of the changes in the GOES-based IFR probabilities shows how IFR conditions evolve over the course of a night.  These changes should be tempered with knowledge of the limitations of the horizontal resolution of GOES that are highlighted in the above imagery.

Fog near San Francisco

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GOES-R IFR Probabilities computed from GOES-West (Upper Left), GOES-West Brightness Temperature Difference (10.7 µm – 3.9 µm) (Upper Right), Suomi/NPP VIIRS Day/Night Band (Lower Left), Suomi/NPP VIIRS Brightness Temperature Difference (10.8 µm- 3.74 µm) (Lower Right), all images near 1000 UTC on March 4 2013.

A high-impact fog event on March 1st led to a Group Stop at SFO International.  The synoptic conditions that supported fog development on 1 March (Images from 1 March are shown at the bottom of this blog post) persisted through the weekend along the West Coast, and fog was again observed on Monday morning, 4 March and the four images above show results from fog detection schemes for that date.  The GOES-R Fog/Low Stratus IFR Probability field shows that the highest probability of IFR conditions is occurring where IFR and near-IFR conditions are observed.  Note the benefits of the high-resolution Suomi/NPP VIIRS data.  Sharp edges to the low cloud field are ably captured in central Santa Clara County.  There are also benefits to using the near infrared and infrared channels to detect regions of low clouds in urban areas, where bright lights can dazzle the Day/Night band so that small breaks in the clouds, as detected just south and west of southern San Francisco Bay, cannot be discerned in the visible.  Compare the differences in the 1-km data from VIIRS to the nominal 4-km resolution of present GOES in the imagery above.  Note also that the brightness temperature difference helps distinguish between snow and clouds over the Sierra Nevada.

GOES-R IFR Probabilities computed from GOES-West, hourly, from 0400 UTC to 1600 UTC on 4 March 2013

The animation, above, of GOES-R IFR Probabilities helps describe and define the region of evolving IFR conditions early on March 4th.

Figures provided by Warren Blier, WFO MTR.

Warren Blier from NWS in MTR sent along an email about the event on March 1st.  The screen capture above shows MODIS-based GOES-R IFR probabilities (on the right) compared with the GOES-West ‘traditional’ unenhanced  brightness temperature difference.  The higher spatial resolution of MODIS and of VIIRS really does pick up the details.  The image below is the 1000 UTC image created using GOES-West data, and the comparison between the MODIS image above and the GOES image below shows the power of MODIS resolution.

GOES-R IFR Probabilities computed using GOES-West data, 1000 UTC on 1 March 2013

An animation of GOES-R IFR probabilities from 0000 through 1600 UTC on 1 March shows the highest IFR probabilities increasing near SFO after 0900/1000 UTC on the first.

Hourly imagery of IFR probabilities computed from GOES-West, 0000 through 1600 UTC on March 1st

IFR conditions in Maine

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GOES-R IFR Probabilities computed from GOES-East (Upper Left), GOES-East Brightness Temperature Difference (10.7 µm – 3.9 µm) (Upper Right), GOES-R Cloud Thickness (Lower Left), Toggle between Suomi/NPP Brightness Temperature Difference (10.8 µm – 3.74 µm) and Day/Night Band “Nighttime Visible” imagery (Lower Right), all around 0815 UTC on 28 February

Weak Low pressure in the Gulf of Maine helped generate IFR conditions over the northeastern United States early in the morning on 28 February 2013.  The brightness temperature difference fields over New England from Suomi/NPP include very sharp cloud edges (also present in the Day/Night band imagery).  Because the GOES-R IFR Probability field also includes information from the Rapid Refresh, it is better able to distinguish fog and low stratus, as present over most of Maine, from elevated stratus, present over western New Hampshire and Quebec.

GOES-R IFR Probabilities computed from GOES-East (Upper Left), GOES-East Brightness Temperature Difference (10.7 µm – 3.9 µm) (Upper Right), GOES-R Cloud Thickness (Lower Left), Suomi/NPP Brightness Temperature Difference (10.8 µm – 3.74 µm) (Lower Right), times as indicated

The animation of the imagery, above, demonstrates how the GOES-R IFR probability product can be used to monitor the evolving nature of a low cloud field.  As the low pressure system in the Northeast starts to move away, the fog/low clouds rotate eastward.   Two noteworthy events in the loop are present.  The 0515 UTC imagery (mislabeled as 0510 UTC), contains stray light in the 3.9 µm field, and the traditional GOES brightness temperature difference field is therefore changed significantly, but the GOES-R IFR probability field is not.  Note also that multiple cloud layers exist over coastal Maine and New Hampshire at the end of the animation, but GOES-R IFR probabilities correctly maintain high probabilities in a region where IFR conditions are present and where the traditional brightness temperature difference field does not show a signal consistent with low clouds.

IFR conditions over the upper Midwest

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GOES-R IFR Probabilities from GOES-East (Upper Left) at 0832 UTC, along with 0900 UTC observations, Traditional GOES-East Brightness Temperature Difference (10.7  µm – 3.9  µm) at 0832 UTC (Upper Right), GOES-R Cloud Thickness computed from GOES-East (Lower Left), Suomi/NPP Day/Night Band Nighttime visible imagery, 0838 UTC (Lower Left)

Stratus and low clouds persisted over western Minnesota and the eastern Dakotas overnight on 25 to 26 February, and the GOES-R IFR Probability field ably captured the region of lowest visibility.  Note that the IFR probability field extends into northwest Iowa (albeit with relatively lower probabilities).  This is a region where high-level cirrus prevents the traditional brightness temperature difference product from giving useful information about the low levels.  In this region, Rapid Refresh data are used to fill in information and more accurately capture the region of IFR conditions.

As above, but for 0802 UTC for GOES-East Products, and with the MODIS-based IFR probability field at 0801 UTC in the lower left

GOES-R IFR Probabilities can be used with MODIS data as well, and the better resolution (1 km at nadir vs. 4 km at GOES nadir) means the MODIS fields have better small-scale detail.    Note, for exanple, the sharper edge to the IFR probability field in east-central Minnesota.

As at the beginning of the post, except for 0415 UTC (top), 0432 UTC (middle) and 0445 UTC(bottom)

Stray-light issues can influence the 3.9 µm imagery, and therefore the brightness temperature difference field, and therefore the GOES-R IFR Probability field.  In the three images above, Stray Light is noteable in the 3.9 µm at 0432 UTC, but that erroneous information can be de-emphasized in the GOES-R IFR probability field because the Rapid Refresh Data in regions where Stray Light is present may show dryer low levels.

Fog and low clouds in the Southeast US

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GOES-R IFR Probabilities computed from GOES-East and Rapid Refresh Data, and surface observations of ceilings and visibility, 0645 UTC-0700 UTC on 11 February (Upper Left), GOES-13 Brightness Temperature Difference, 0645 UTC (10.7 µm – 3.9 µm) (Upper Right), Suomi/NPP VIIRS Brightness Temperature Difference (10.8 µm – 3.74 µm) at 0638 UTC (Lower Left), Suomi/NPP Near IR Imagery (3.74 µm) at 0638 UTC (Lower Right)

The image above is a good example of the importance of fused data in many fog/low stratus events.  The near IR imagery, bottom right, shows many different cloud layers.  A strong storm moving towards the East Coast on Monday morning 11 February generated many cloud layers that make the traditional method of fog detection, the brightness temperature difference between 10.7 µm and 3.9 µm, problematic.  Adding information from the model, however, allows the GOES-R product to identify the region of IFR conditions that extends northeastward from central Georgia to central Virginia.

Fatal Crash on I-16 in Georgia: Was it fog-related?

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Map of Crash Location, courtesy WMAZ TV in Macon, Georgia

A multi-vehicle accident with fatalities occurred in extreme western Laurens County in central Georgia early Wednesday Morning, 6 February 2013.  (According to this news report, the first crash was around 1310 UTC)  Was fog a factor in this accident?  Fog was reported in and around the scene as first responders arrived.

Laurens County is in the Peachtree City CWA, and the relevant part of the Forecast Discussion at 0000 UTC is as follows:  

000
FXUS62 KFFC 060007
AFDFFC

AREA FORECAST DISCUSSION...UPDATED FOR AVIATION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
ISSUED BY NATIONAL WEATHER SERVICE BIRMINGHAM AL
705 PM EST TUE FEB 5 2013

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...

FAIRLY QUIET WEATHER THROUGH THE SHORT TERM PERIOD. A WEAK
SHORTWAVE HAS BROUGHT A BAND OF CLOUDS TO THE AREA AND A FEW
SPRINKLES SHOW UP EVERY NOW AND THEN ON RADAR. CLOUDS ARE EXPECTED
TO THIN OUT OVERNIGHT AND FOG COULD BECOME AN ISSUE IN THE FEW
HOURS BEFORE SUNRISE. THIS IS SOMETHING THAT WILL HAVE TO BE
MONITORED THROUGH THE EVENING. MILD TEMPERATURES THROUGH THE
PERIOD.

.LONG TERM /THURSDAY THROUGH TUESDAY/... 
[...snipped...]
&&

.AVIATION... 00Z TAF DISCUSSION.

VFR CIGS WILL CONTINUE ACROSS THE TAF SITES THIS EVENING.
EXPECT MVFR CONDITIONS LATE TONIGHT AS FOG AND LOW CLOUDS DEVELOP
BEGINNING AFTER 06Z NEAR CSG SPREADING NORTH AND EAST. THE ATLANTA
TAF SITES SHOULD EXPECT TO BE IMPACTED BY 08-09Z. IMPROVING
CONDITIONS BY 15Z. LIGHT WESTERLY WINDS EXPECTED. 
 
 So, overnight fog was considered a possibility at 0000 UTC.
And updated AFD was issued shortly before 0600 UTC.  In that update the Aviation discussion was tweaked:
FXUS62 KFFC 060553
AFDFFC

AREA FORECAST DISCUSSION...UPDATED FOR AVIATION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
ISSUED BY NATIONAL WEATHER SERVICE BIRMINGHAM AL
1245 AM EST WED FEB 6 2013

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... 
 
[...no changes...]
 
.LONG TERM /THURSDAY THROUGH TUESDAY/... 
 
[...snipped for brevity...]
&&

.AVIATION... 06Z TAF DISCUSSION.

PATCHY CEILINGS BKN030-040 LINGERING THROUGH THE NIGHT. POTENTIAL
FOR LIFR CONDITIONS WHERE SKIES ARE CLEAR...BUT EXPECT ALL TAF SITES
TO HAVE AT LEAST MVFR CONDITIONS 08Z THROUGH 14Z. IMPROVING AFTER
THAT TO VFR. WINDS NORTHWEST 5 TO 10KT AFTER 15Z.


//ATL CONFIDENCE...06Z UPDATE...
MEDIUM CONFIDENCE ON ALL ELEMENTS.
 Note that a mention of LIFR conditions has appeared in the Aviation Discussion.  What did the GOES-R IFR Probability show between 0000 and 0600 UTC?
GOES-R IFR Probabilities computed from GOES-East and Rapid Refresh Data, 0115 through 0515 UTC 6 February, along with hourly observations of ceilings/visibility
Especially in the last two hours — 0415 and 0515 UTC — there is a general expansion in high probabilities from west to east across southern Georgia, with probabilities increasing north of I-16.  By 0815 UTC, below, IFR conditions are being reported at many locations in northwest Georgia, and IFR probabilities continue to increase over east-central Georgia.
As in the loop above, but for 0815 UTC only.  Interstate Highways are denoted in Blue.
The AFD issued at 0930 coincided with the issuance of a dense fog advisory (highlighted in red) for most of the CWA:

000
FXUS62 KFFC 060930
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
430 AM EST WED FEB 6 2013

.SHORT TERM /TODAY THROUGH THURSDAY NIGHT/...
SOME LOW LEVEL MOISTURE REMAINING THIS MORNING AND THIS HAS PRODUCED
FOG ACROSS MANY AREAS. WILL GO AHEAD AND ISSUE A DENSE FOG ADVISORY
SINCE MOST PLACES SEEM TO BE HEADED FOR VERY LOW VISIBILITY.
OTHERWISE DRY HIGH PRESSURE BUILDING OVER THE SOUTHEAST TODAY AND
MOVING OFF THE ATLANTIC COAST TONIGHT. NEXT SHORT WAVE COMING ACROSS
THE NORTHERN GULF SHOULD BEGIN TO AFFECT OUR CWA MAINLY 06Z THURSDAY
AND BEYOND. THIS SOUTHERN STREAM SYSTEM MOVES ACROSS THE STATE
THURSDAY AND THURSDAY NIGHT WITH SOME DIFFERENCES BETWEEN MODELS
WITH LOCATION AND STRENGTH OF SURFACE LOW. IN GENERAL...LOOKS LIKE A
WEDGE SETTING UP LATE TONIGHT INTO THURSDAY WITH MUCH OF THE CWA IN
EASTERLY FLOW. THERE SHOULD BE A SHARP GRADIENT OF TEMPERATURES
BETWEEN NORTH AND CENTRAL ZONES AND FOR NOW HAVE KEPT THE WARMER AIR
ON THURSDAY CONFINED TO COLUMBUS TO MACON AND SOUTH. CATEGORICAL
POPS FOR THURSDAY TAPERING OFF WEST TO EAST THURSDAY NIGHT AS THE
SURFACE LOW MOVES EAST. NO MENTION OF THUNDER AS WEDGE SHOULD BE
STABLE. HOWEVER SOME INSTABILITY COULD PUSH INTO THE CENTRAL ZONES
THURSDAY AFTERNOON ALONG THE BOUNDARY.

41


.LONG TERM /FRIDAY THROUGH TUESDAY/... 
[...snipped...] 
01

&&

.AVIATION...
06Z TAF DISCUSSION.
PATCHY CEILINGS BKN030-040 LINGERING THROUGH THE NIGHT. POTENTIAL
FOR LIFR CONDITIONS WHERE SKIES ARE CLEAR...BUT EXPECT ALL TAF
SITES TO HAVE AT LEAST MVFR CONDITIONS 08Z THROUGH 14Z. IMPROVING
AFTER THAT TO VFR. WINDS NORTHWEST 5 TO 10KT AFTER 15Z.

//ATL CONFIDENCE...06Z UPDATE...
MEDIUM CONFIDENCE ON ALL ELEMENTS.

41

&&

.PRELIMINARY POINT TEMPS/POPS... 
[...snipped...]
 &&

.FFC WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR THE FOLLOWING
ZONES: BALDWIN...BANKS...BARROW...BARTOW...BIBB...BLECKLEY...
BUTTS...CARROLL...CATOOSA...CHATTAHOOCHEE...CHATTOOGA...
CHEROKEE...CLARKE...CLAYTON...COBB...COWETA...CRAWFORD...CRISP...
DADE...DAWSON...DEKALB...DODGE...DOOLY...DOUGLAS...EMANUEL...
FANNIN...FAYETTE...FLOYD...FORSYTH...GILMER...GLASCOCK...
GORDON...GREENE...GWINNETT...HALL...HANCOCK...HARALSON...
HARRIS...HEARD...HENRY...HOUSTON...JACKSON...JASPER...
JEFFERSON...JOHNSON...JONES...LAMAR...LAURENS...LUMPKIN...
MACON...MADISON...MARION...MERIWETHER...MONROE...MONTGOMERY...
MORGAN...MURRAY...MUSCOGEE...NEWTON...NORTH FULTON...OCONEE...
OGLETHORPE...PAULDING...PEACH...PICKENS...PIKE...POLK...
PULASKI...PUTNAM...ROCKDALE...SCHLEY...SOUTH FULTON...SPALDING...
STEWART...SUMTER...TALBOT...TALIAFERRO...TAYLOR...TELFAIR...
TOOMBS...TOWNS...TREUTLEN...TROUP...TWIGGS...UNION...UPSON...
WALKER...WALTON...WARREN...WASHINGTON...WEBSTER...WHEELER...
WHITE...WHITFIELD...WILCOX...WILKES...WILKINSON.

&&

$$

SHORT TERM...41
LONG TERM....01
AVIATION...41

The animation from 0815 UTC through 1315 UTC shows a continued increase in the probabilities over the crash site on I-16.  In addition, observations decrease to IFR conditions.  Note that at 1315 UTC the switch between nighttime and daytime predictors is present in the image as a southwest to northeast boundary over extreme eastern Georgia.  Probabilities are high over the crash site, but by 1415 UTC, they have all but vanished as the fog quickly dissipated at sunrise.  This suggests a fog that is not thick, and the GOES-R Cloud Thickness corroborates this assumption (see below)

As in the loop above, but from 0815 UTC through 1315 UTC.  Crash occurred at 1310 UTC
GOES-R Cloud Thickess just before Twilight Conditions, 1215 UTC 6 February.  Values near the Crash Site are 600-700 feet.
The Cloud Thickness field, above, at 1215 UTC, just before twilight conditions, shows values around 600 to 700 feet.  This chart suggests a rapid dissipation time of around 1 hour.  Indeed, visible imagery around  sunrise shows scant evidence of widespread fog.
Zoomed-in GOES-13 Visible Imagery over east-central Georgia, times as indicated.  Montrose (Yellow square) is indicated within Laurens County (outlined in green)
Polar orbiters also provide information — at higher spatial resolution — about the evolving situation overnight.  Suomi/NPP made two passes over Georgia between 0600 and 0900 UTC, and the brightness temperature difference product that was produced is shown below.    There is a noticeable increase in water clouds over Georgia between 0632 UTC and 0811 UTC, the times of the images.

Suomi-NPP Brigthness Temperature Difference (10.80 µm- 3.74 µm) at 0632 UTC and 0811 UTC.  Interstate 16 crosses Laurens County near the center of these images.

MODIS data from Aqua were used to produce IFR probabilities at 0645 UTC, below.  This was before the most fog had developed, but it does confirm the picture painted with GOES data’s broader brush:  IFR probabilities are increasing over Georgia.

MODIS-based GOES-R IFR Probabilities over Georgia, 0645 UTC on 6 February 2013.

Finally, AVHRR data from NOAA-15 from 1015 UTC show widespread stratus extending eastnortheast from southwest Georgia to central Georgia.

Brightness Temperature Difference (10.8 µm – 3.74 µm) from AVHRR data, 1028 UTC 6 Feb 2013

California Fog

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GOES-R IFR Probability computed from GOES-West (Upper Left), GOES-R Cloud Thickness computed from GOES-West (Lower Left), GOES-West Brightness Temperature Difference (10.7 µm – 3.9 µm) (Upper Right), GOES-West 10.7 µm imagery (Lower Left) at 0400 UTC 4 February

Fog develped over the San Joaquin and Salinas Valleys of California early on 4 February.  At 0400 UTC, the Brightness Temperature Difference signal shows a noisy signal over the east part of the San Joaquin Valley, with a more coherent signal off the coast and over Kern and Kings County.

As above but at 0900 UTC.

By 0900 UTC, five hours later, although the seemingly noisy signal continued over the California in the brightness temperature difference product, the GOES-R IFR probability field is starting to show higher values aligned through the San Joaquin and Salinas Valleys, where IFR conditions have developed.

As above, but at 1200 UTC

At 1200 UTC, above, high IFR probabilities extend through the Salinas Valley and in the San Joaquin valley where IFR conditions are noted.  IFR probability is also high over San Francisco Bay where marine stratus has moved inland.

As above, but at 1500 UTC

The regions of reduced visibility continue at 1500 UTC, the last image before twilight conditions disallows computation of Cloud Thickness (indeed, the terminator is apparent in the image).  The cloud thickness of 1100 feet suggests, based on this scatterplot, a dissipation time of around 4 hours.  The animation below shows visible imagery at 1730, 1830 and 1930 UTC that aligns with the predictions.

GOES-15 0.62 µm Visible Imagery, times as indicated.

Suomi/NPP VIIRS data overflew this region twice during the night, and provided brightness temperature difference information at high spatial resolution.  The GOES-R IFR algorithm is not yet applied to Suomi/NPP data (like it is to MODIS data) however.

As at top, but with Suomi/NPP Brightness Temperature Difference (10.8 µm – 3.74 µm) in the lower right, at ~0900 UTC.
As above, but at 1030 UTC.