August 9, 2012 GOES-R FLS

This was my first exposure (shift) with GOES-R material (luck of the draw?).  Appreciated the lesson and learned a lot. I was impressed with the probability FLS image and comparing it to the older satellite images of low clouds/stratus.  I can see the utility with generating the TAFS...the FLS product will give me more confidence to go or not go with fog/stratus IFR conds.  The limitations at twilight were explained....makes sense.  Always great to have more tools at our disposal!

Some examples of the FLS probability product are shown in central Indiana. In Fig. 1, you can see a known characteristic with the cloud depth product, wherein the cloud phase product shows ice-based clouds "blacked out".  This is a result of the cloud depth product being limited to water-based clouds.  Also, note in Fig. 1 a swath of greater than 50% prob is located in east central IN. The nearest stations are showing CIGs of 110 and 95 hft and are outside this yellow swath.

Fig. 1. 1302Z: Cloud depth, IFR FLS Product, VIS Sat, GOES Cloud type(from top-left going clockwise).

In Fig. 2, the FLS product is now showing high probability of fog or low-level stratus.  However, the obs in the center of this high probability swath is reporting clear skies at 10 SM visibility.  Vis satellite was inspected and it reveals broken-overcast skies in this swath of high probabilities.  This was an interested feature given the initial discrepancies between the observations and the FLS product.  However, it was noted that the report of the obs was 1353 Z.  Wherein the satellite products have a time stamp of 1332. Thus, this is more so an artifact of this case (postmortem), where the observations and satellite products are not synchronized.  In a real-time situation, this is not anticipated to be an issue.

Fig. 2. 1332Z: Cloud depth, IFR FLS Product, VIS Sat, GOES Cloud type(from top-left going clockwise).

 In Fig. 3, the FLS product time stamp is 1402, which is now better aligned with this aforementioned METAR report at 13:53.

Fig. 3. 1402Z: Cloud depth, IFR FLS Product, VIS Sat, GOES Cloud type(from top-left going clockwise).

Further to the west, over the MKX WFO the GOES-R FLS IFR product performed well depicting the gradient in ceilings.  With low probabilities along a Madison to Milwaukee line; but increasing probabilities towards Wisconsin Dells  to West Bend.  Fig. 4 illustrates that the higher IFR probabilities to the north indeed matchup with lower ceilings, around 500 feet.  The ceilings over Milwaukee and Madison were 2700-4300 feet.

Fig. 4 1332 UTC Cloud depth, IFR FLS Product, GOES VIS, Heritage Fog GOES BTD(from top-left going clockwise).

To the northwest, the GOES-R FLS IFR probabilities captured a small, yet operationally significant area of low ceilings near and east of Fargo, ND  (Fig. 5).  The surface observations agree with the higher probabilities with 500-900 foot ceilings.

Fig. 5 1132 UTC Cloud depth, IFR FLS Product, GOES VIS, Heritage Fog GOES BTD (from top-left going clockwise).

It should be noted AWIPS @ MKX has been rolled back to an older version in preparation for upgrades to AWIPS-II.  As such, the products and enhancements are not current.

Ed Townsend - MKX
Rusty Kapela - MKX
Justin Sieglaff - CIMSS

Marine Fog Near California

Marine fog was clearly apparent along the California coastline with the GOES-W 11-3.9 micron satellite channel difference imagery (above) on the morning of Tuesday, August 16, 2011. In fact, we could see fog or low clouds that spread inland near Los Angeles and became trapped against the San Gabriel Mountains.

The SSEC CIMSS GOES-W MVFR Probability product (above) showed 70-75% probability of MVFR ceilings occurring in this region, with higher probabilities further north, off the coast of San Francisco . The SSEC CIMSS GOES-W IFR Probability product (below) showed 40 to 50% probability of IFR ceilings near Los Angeles, with up to 75% near San Francisco. These products both captured the fog that was trapped up against the San Gabriel mountains very well.

The surface observations (overlaid on the satellite products) showed dense fog (1/4 statute mile visibility and vertical visibility of 100 feet) at Catalina Airport on the island, and fog (2 1/2 statute mile visibility and vertical visibility of 500 feet) at Los Angeles Airport (KLAX). Other observations just inland of LAX had MVFR visibility and 500 to 1000 foot ceilings. San Francisco had 200 foot ceilings, lower than those at LAX.

The MVFR and IFR Probability products captured the marine fog very well, spatially. Quantitatively, it tended to be underestimated near the Los Angeles area. Due to the lack of observations offshore, it was difficult to discern between low stratus and fog that we could see in the satellite imagery. Therefore, we could not fully evaluate how well the MVFR vs IFR Probability products captured the event, but we could still infer their validity.

From a short-term forecasting standpoint, we already know we have low ceilings, but it would be very useful to know how deep the fog or low cloud area actually is so that we can determine how long it will be before it can burn off/mix out. We can use NWS soundings, data from aircraft, or other data that may be available at various points that are typically far apart. However, the SSEC CIMSS group has this Fog Depth product that can show from a satellite point of view how thick the fog/low stratus is (see image below). In this image, the fog depth was about 1115 to 1175 feet thick near Los Angeles.

This NWS sounding from KNKX San Diego (above) shows the top of the marine layer was at about 1500 feet AGL, very similar to what the Fog Depth product showed.

I know I will use this product when dealing with fog in the Great Lakes Region when I'm on the short-term forecast desk.

Submitted by Marcia Cronce (NWS) and Dan Hartung (SSEC CIMSS)