Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Huntsville Alabama
156 am CDT Wednesday Aug 20 2014
we will be monitoring convective trends during the next few hours as
the rap continues the trend of the NAM of the past few days at
forecasting nocturnal convection from middle Tennessee into northern Alabama. In fact,
infrared imagery and observation indicate some cumulus development across portions of
our forecast area. Storm Prediction Center mesoanalysis indicated MUCAPES of 3000-4000
j/kg across the region (and even higher to our west). The ohx 00z
radiosonde observation indicated this as well, above a capping inversion. The
convection will likely fire just above the cap as a low level jet of 25-30kt
develops. If storms fire, they could become strong to severe rather
quickly, despite limited wind shear.
Storms are prognosticated to decay this morning as they migrate S-se. The
capping inversion will likely suppress convection for most of the
area today. The "edge" of the cap appears to be depicted by the NAM
quantitative precipitation forecast from middle Tennessee into northern Georgia late this afternoon and evening, possibly
just clipping our eastern counties. For now, have maintained a schc
pop for the area for both this morning and possible afternoon
convection. The day shift may be able to trim this back in our
western zones as trends become better defined.
Synoptically, the forecast has not changed much with a large upper
ridge building over the central Gulf states during the latter half of
the week, expanding north and west with time. This will result in the
longest heat wave of the Summer thus far. Weak northerly 500 mb flow
will bring weak narrow shortwaves over the ridge and into the southeast. The
cap is expected to suppress deep convection, so will keep a dry
forecast going. Despite the building ridge, the GFS/ec MOS appear a
bit too warm given past performance, and will side with the NAM in
the short term, and adjust downward slightly in the medium range
forecast. With time, deeper mixing will lower afternoon dew point values.
Heat index values will likely fall short of heat advisory criteria
during this period. However, the main hazard will be the longevity of
the heat wave. This will be especially apparent since we have had a
very cool Summer to this point.
/issued 1225 am CDT Wednesday Aug 20 2014/
for 06z tafs...no changes to previous aviation forecast reasoning.
There is still uncertainty regarding potential development of thunderstorms and rain
towards sunrise. Although most activity will remain North/East of the
terminals...amds may be required to introduce thunderstorms in the vicinity/cumulonimbus between 10-14z.
Clouds will increase overnight as an upper air disturbance passes by
to the NE...with broken layers of SC/ac between 3500-8000 feet. A lower layer
of stratocu may also develop around 1500 feet...with potential for
reduced visibility in br around sunrise. VFR conds are expected tomorrow...
with scattered high-based cumulus and a west flow of 5-10 kts -- backing to south-southwest
Preliminary point temps/pops...
Huntsville 93 71 93 72 / 20 0 0 0
Shoals 94 72 94 73 / 20 0 0 0
Vinemont 93 74 94 76 / 20 0 0 0
Fayetteville 91 69 91 72 / 20 0 0 0
Albertville 93 71 94 73 / 20 0 0 0
Fort Payne 93 69 93 73 / 20 0 0 0
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