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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 151112

Area Forecast Discussion
National Weather Service Huntsville AL
612 AM CDT Mon Oct 15 2018

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 347 AM CDT Mon Oct 15 2018

The forecast area is in between a building ridge centered across FL,
and an amplified, positively tilted trough moving into the Great 
Lakes. A lingering boundary to our northwest will continue to bring
showers this morning, with higher POPs across NW AL and Southern 
Middle TN (much like yesterday). As the sfc low scoots east of the 
Great Lakes, it will pull the associated cold front southeast into 
the region later this afternoon. Ahead of the front, there will be 
some isentropic lift and winds will become southerly, increasing 
showers to become scattered areawide with the increase of moisture 
and temps. Cannot rule out a rumble of thunder so included isolated 
thunder chances in for this afternoon. Daytime highs reaching the 
upper 70s (maybe 80 degrees), will be the warmest in the forecast 
package. The front will move through fairly quick and behind the 
front, winds will become northwesterly and increase to ~10mph with 
gusts ~15mph.

.SHORT TERM...(Tonight through Wednesday Night)
Issued at 347 AM CDT Mon Oct 15 2018

Northwesterly winds will filter in cooler air behind the front,
getting overnight lows down into the lower 50s across NW AL and 
Southern Middle TN and into the upper 50s across NE AL. Precip
chances will linger into tonight, but become more isolated later

On Tuesday, the front will be south of the forecast area but we will
still be in between the ridge to our southeast and a trough to our
north. The southwesterly flow aloft will stream disturbances into 
the TN Valley and combined with isentropic lift, precip chances will
increase through the day. Kept a slight chance of rain going in early
Wednesday to accommodate the discrepancy between the GFS that clears
out the precip faster than the ECMWF. Conditions will be dry, and 
cooler, by Wednesday afternoon with decreasing cloud cover. Daytime 
highs will be in the mid 60s and overnight lows will dip into the 
upper 40s as skies become mostly clear. 

.LONG TERM...(Thursday through Sunday) 
Issued at 347 AM CDT Mon Oct 15 2018

Upper level ridging will in place over the SE North American domain
on Thursday. This ridge will weaken somewhat during the course of the 
remainder of the week, as troughing in the northern stream begins to 
sharpen during the weekend. The amplification of the trough in part 
will be caused by an upper disturbance/speed max moving across
British Columbia Wed/Thu, merging with energy ejected from an upper
low over the Intermountain West. There was reasonable inter-model 
agreement from the GFS, ECMWF, Canadian into next Sunday regarding 
their respective forecasts of the 500mb level. At the surface, high 
pressure layered over the Ohio Valley will move eastward, resulting 
in NE winds on Thursday becoming east, then SE on Friday. This will 
gradually bring additional lower level moisture across the southeast
CONUS and rain chances - just in time for the weekend.

The deterministic models were good agreement with rain chances late
Friday and on Saturday. Following them, have lower end rain chances 
starting Friday afternoon for our Tennessee counties and along the 
far northern Alabama border region. Better chances for showers are 
expected Friday night and Saturday morning, as a cold front pushes in
a NW-SE manner across the forecast area. Post frontal showers 
occurring north of the boundary will gradually end from north to 
south as colder and drier air slowly filters in. Although there was
shear preceding/accompanying the front, not enough instability was
present, therefore kept thunder out of the forecast.

Daily high temperatures in the extended will trend below seasonable
norms. Highs on Thu/Fri will range in the upper 60s to around 70, 
below average highs of around 74. Highs in the mid 60s Saturday will
cool to around 60 on Sunday. Night time lows above normal Thursday 
and Friday nights (around 50) will cool into the mid 40s for Saturday
night. Lows nearing 40 look possible Sunday night, with a few upper 
30s in those normally colder spots. 


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 612 AM CDT Mon Oct 15 2018

VFR conditions will start off the TAF period. As a cold front pushes
into the area, ~18/19Z CIGS will fall into lower MVFR category 
(1500-2000ft) and VCSH begins. Northerly winds will increase behind 
the front ~10kts, showers taper off, and CIGS remain in MVFR, 
however will not rule out the chance they fall into IFR temporarily.
Most models agree that CIGS will remain low-end MVFR til the end of 
the TAF period, but they do not agree on timing for rainfall to 
return so kept a mention of rain returning out for this TAF 





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