Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 231136

Area Forecast Discussion
National Weather Service Huntsville AL
536 AM CST Thu Jan 23 2020

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 315 AM CST Thu Jan 23 2020

Latest water vapor imagery shows a trough digging into the Plains,
with southwesterly flow over the TN Valley. Surface winds are slowly
veering to the southeast this morning, which will help filter more
moisture into the lower levels. Near term guidance is fairly
consistent on an initial round of showers moving across our eastern
areas during the mid to late morning hours, as insentropic lift
increases. While southwesterly flow continues to bring moisture into
the mid levels, the low levels remain fairly dry as dewpoint
depression are around 15 to 20 degrees. As low level flow veers to
the southeast after sunrise, profiles become fully saturated and
light showers may develop over areas along and east of I-65. This
will quickly move east of the area, before the main batch of showers
moves into the area.

The aforementioned trough will continue to move eastward through the
day, with a surface front trailing from its parent low over the Mid
Mississippi Valley. Widespread showers ahead of this front will push
into our western counties this afternoon and continue to move
eastward across the area. Temperatures will be fairly mild through
the day. With temps starting off in the upper 30s to lower 40s,
expect highs to warm into the upper 40s with the cloud cover and rain
preventing much heating.

.SHORT TERM...(Tonight through Saturday night)
Issued at 315 AM CST Thu Jan 23 2020

The upper trough over the Plains will move into the Mississippi
Valley tonight, with the surface low traversing the Ohio Valley and
bringing its cold front through the forecast area during the
overnight hours. Widespread showers will continue through the evening
and into the early part of Friday morning, before rain tapers off
with the passage of the cold front. The upper low will move just to
the north of the area, with some moisture wrapping around its western
and southern periphery. Guidance still keeps this moisture north of
the area, but isolated locations across our extreme northern areas
may see an additional round of light rain Friday night.

The trough/low will move east of the area on Saturday, with flow
aloft becoming zonal. This westerly flow will keep conditions mild
over the TN Valley. Temperatures will only warm into the mid to upper
40s once again, with overnight lows Saturday night falling into the
lower 30s.

.LONG TERM...(Sunday through Wednesday)
Issued at 315 AM CST Thu Jan 23 2020

Forecast confidence drops quite a bit heading into the long term
period, as guidance really begins to diverge of their solutions of
the synoptic pattern over the region. A shortwave is expected to dig
southward from the Northern Plains and move into the Lower
Mississippi Valley by Sunday morning. Models differ on how far south
the trough moves, with the ECMWF pushing the trough along the Gulf
Coast and the GFS bringing it through the TN Valley. The GFS solution
would bring a greater coverage of light showers over the area
beginning Sunday night and continuing through Monday, while the ECWMF
keeps the moisture and showers south of the area. With either
solution, the trough will exit the area by Monday morning, with dry
conditions in place for the start of the new work week. Given the
discrepancies and uncertainty, have kept only slight chance mention
in the forecast.

After a dry and mild start to the week, another trough is expected to
move from the Four Corners region, eastward through the Mid/Lower
Mississippi Valley. Upper ridging will slide east and through the TN
Valley Monday night and Tuesday, with flow aloft becoming
southwesterly by Tuesday afternoon. Similar to the Sunday/Sunday
night shortwave, forecast guidance differs on the track of the trough
and its surface low. The ECMWF is much stronger with the upper
trough and surface low, while the GFS keeps several weak shortwaves
moving through more zonal flow aloft. Again, given the uncertainty,
will maintain blended guidance which suggests a slight chance of
showers beginning Tuesday night and increasing in coverage during the
day Wednesday.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 536 AM CST Thu Jan 23 2020

Low clouds, ~2500 feet, will move into the region, impacting the
KMSL and KHSV terminals by 15Z. Flight conditions will continue to
deteriorate through the day as a cold front approaches the area.
Confidence on exact timing and height of the low clouds is not overly
high, however expect IFR conditions to impact the area by 19Z. LIFR
conditions are possible during the afternoon hours, but again,
confidence is not high enough to include these cigs in the forecast.
Light to moderate rain is also expected after 20Z, which will likely
reduce visibilities to between 2 and 4SM. Additionally, some of the
heavier showers may lead to ponding of water on runways, especially
during the late afternoon and early evening hours. IFR conditions
will persist into the overnight period, with LIFR conditions possible
after 08Z.





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