Birmingham, Alabama Surprise Snow of January 28, 2014…Or Was It?

GOES IR (left), NESDIS Snowfall Rate Product (center) and Composite NEXRAD Base Reflectivity (right)           for around 1045 UTC 28 January 2014.

GOES IR (left), NESDIS Snowfall Rate Product (center) and Composite NEXRAD Base Reflectivity (right) for                 around 1045 UTC 28 January 2014.

In the early morning hours of 28 January (approximately 1047 UTC or 4:47 AM CST), the Operational NESDIS Snowfall Rate Product (SFR; above center), that uses the Advanced Microwave Sounder Unit (AMSU-A) and Microwave Humidity Sounder (MHS) on-board four Low Earth Orbiting (LEO) NOAA POES and EUMETSAT Metop satellites to produce a liquid equivalent snowfall rate over land, was detecting snow in the clouds over Central Alabama (red circle) and an area from northern Mississippi into Central Tennessee (yellow oval).   In both areas there was some enhanced cooler cloud tops on the geostationary infrared imagery (above, left) and light precipitation  detected by the composited NEXRAD base reflectivity (above, right) in approximately the same area that the SFR was detecting snow in the clouds.  However, the only snow being observed (light snow at that) at the surface at the time was in Northwest Mississippi at Tunica Municipal Airport.  The SFR has a known high bias for sensing low liquid equivalent rates/light snow and so forecasters need to understand that just because the product is sensing snow in the clouds, the relatively low moisture that may exist close to the surface at the start of an event can initially prevent the precipitation from reaching the ground.  Now let’s focus on the Central Alabama snow being detected by the SFR at 1047 UTC in the enhanced satellite geostationary IR cloud tops and aloft by the radar.  At this time no snow was being observed around the Birmingham, Alabama area.  Still the SFR would have provided valuable information to forecasters that the snow detected in the clouds could be seeding existing clouds (a precursor) and with increased moisture more easily support snow eventually reaching the ground later in the morning.   This is what actually occurred as Birmingham-Shuttlesworth International Airport started to observe snow reaching the ground shortly before 16 UTC (10 AM CST) and was confirmed by the approximate 1615 UTC SFR (below, center), GOES IR (below, left) and composite NEXRAD (below, right) imagery/data; about 5 hours after the 1047 UTC SFR was detecting snow in the clouds.   NESDIS researchers and analysts are carefully looking at the SFR product’s sensing of the snow in the cooler enhanced IR cloud tops as a precursor to snow eventually reaching the ground; thus helping alert forecasters to the impending snow reaching the ground.  And in this case once the snow started reaching the ground in the Birmingham area just before 16 UTC, its intensity increased through the rest of the morning and into the afternoon on the 28th (snow-water equivalent reached 0.03″ through 18 UTC and an additional 0.05″ fell between 18 and 21 UTC .

Approximate 1615 UTC GOES IR (left), Snowfall Rate Product (center), NEXRAD Composite Base Reflectivity (right)

GOES IR (left), NESDIS Snowfall Rate Product (center), Composite NEXRAD Base Reflectivity (right) for                        around 1615 UTC 28 January 2014. Black Circle depicting snow in and around Birmingham, Alabama.

 

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