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Synthetic low cloud / fog imagery to forecast stratus

Posted On: September 25, 2012 - By: Dan Bikos


The synthetic low cloud / fog product from the NSSL WRF-ARW model has a variety of forecasting applications.  One of those is forecasting the development of stratus clouds.

The NWS forecast office in Austin / San Antonio made use of this product for the above mentioned application on September 23:

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX

626 PM CDT SUN SEP 23 2012

AVIATION…

CONVECTION ALONG THE SEA-BREEZE BOUNDARY WILL REMAIN SOUTH OF KSSF AND KSAT AND WILL DISSIPATE AFTER SUNSET WITH THE LOSS OF DAYTIME HEATING. OTHERWISE THE CU FIELD THIS AFTERNOON IS AN INDICATION OF INCREASING LOW LEVEL GULF MOISTURE ACROSS SOUTH CENTRAL TEXAS. THE 18Z NAM X-SECTIONS DEPICT GOOD MOISTURE BELOW 925MB AT KSAT AND KSSF BUT SHALLOWER AT KAUS AND SOMEWHAT DRIER AT KDRT. THE 12Z CIRA WRF SIMULATED FOG/LOW CLOUD PRODUCT IS VERY BULLISH ON STRATUS FORMATION OVERNIGHT. WE HAVE HAD GOOD RESULTS WITH THIS EXPERIMENTAL PRODUCT AND THE TERMINAL FCSTS WILL BE BASED ON ITS SOLUTION. MVFR CIGS WILL REACH KSSF AROUND 09Z…KSAT AT 0930Z AND KAUS BY 12Z. THE STRATUS WILL ALSO SPREAD WESTWARD REACHING KDRT BY 13Z. THE STRATUS WILL LIFT AND MIX OUT WITH VFR CONDITIONS PREVAILING BY 16Z.

Here is the synthetic low cloud / fog product that is the discussed above:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/24sep12_syn_fog&image_width=1020&image_height=730

In this color table, low cloud / fog shows up as blue.  The expanding blue region over southern and central Texas corresponds to the model forecasting the development of low cloud / fog.

As verifying observations, we will make use of the GOES low cloud / fog product with corresponding visibility (bottom number, miles) and ceiling (top number, hundreds of feet AGL) observations:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/24sep12_sw_albedo&image_width=1020&image_height=730

In this color table, low cloud / fog corresponds to the grey / dull white region in south / central Texas.  The stratus clouds were forecast over approximately the same area in Texas that was forecast by the model, and dissipation commencing at about the same time (around 16 Z)

The real-time imagery described above can be found on the GOES-R Proving Ground Real-time Products page.


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