Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 211505

Area Forecast Discussion
National Weather Service Huntsville AL
1005 AM CDT Wed Mar 21 2018

.NEAR TERM...(Rest of Today)
Issued at 1005 AM CDT Wed Mar 21 2018

Quiet and seasonably cool weather conditions prevail across the cntrl
TN Valley this late Mon morning. Temp trends have managed to climb
into the upper 30s/lower 40s for most locations, and with skies
expected to be partly cloudy over most of the area, these values
should be able to climb above the 50F mark going into the afternoon
hrs. Light returns on area radars earlier this morning have also
weakened or moved E of the area. This activity may have resulted in
a few flurries mainly across a few portions of mid/E TN. High
pressure out of the Plains states though will be moving into the
region later today, aiding with the quiet wx pattern. Other than
removing the slight chc for light rain/snow from parts of srn mid TN,
no major changes were needed to the ongoing forecast attm.

.SHORT TERM...(Tonight through Friday Night)
Issued at 340 AM CDT Wed Mar 21 2018

Winds should diminish fairly quickly tonight as we cool off after
sunset and surface high pressure starts to build in from the west.
Although we won`t see calm winds tonight, the combination of clear
skies, winds less than 5 mph and dew points dropping into the mid
20s, will allow low temps to drop to below freezing, upper 20s to
around 30. Therefore, and in coordination with the neighbors, will
issue a freeze warning from 7z/2am to 13z/8am for the entire area.
Some areas may not see a full three hours below freezing but it is
widespread enough that the freeze warning is warranted.

With the high pressure in place Thursday and a developing mid level
ridge pressing in from the west, we should see sunny skies and highs
in the mid to upper 50s with winds less than 10 mph.

A mid and upper level ridge strengthens significantly over the
intermountain west Thursday night as a low deepens over the
northeast. This will create a pretty strong upper level jet oriented
more north to south stretching from MN down through GA. This lift
combined with a slight increase in mid level moisture has allowed
guidance to show some light QPF tracking into our area between 6-12z
Friday morning. Guidance has backed off in the last two days with
this, leaving only the NAM with any QPF. Will pull back the pops from
the last forecast and leave it only in northeastern areas since the
mid level lift isn`t too strong and there really isn`t much moisture.
Lows will be warming into the upper 30s/lower 40s so it should be
all rain and maybe a few snow flurries in S. middle TN, if anything.

Guidance is also coming in drier for Friday and Friday night likely
due to the lack of any appreciable lift and only a mid level layer of
moisture, so just enough for a mostly cloud day. Removed any pops
from Friday but will leave them in for Friday night as a surface low
starts to develop over KS/MO. This will start to extend a frontal
boundary to our area by 9-12z Friday night/Saturday morning. With
lows Friday night in the 40s, it will be all rain. Highs on Friday
will warm into the lower 60s.

.LONG TERM...(Saturday through Tuesday)
Issued at 340 AM CDT Wed Mar 21 2018

Most guidance moves the surface low from Missouri southeast into
northwestern Tennessee on Saturday. A boundary extends southwest from
the surface low into northeastern Texas. Good shear and low level
helicity will be in place over the area ahead of this boundary, as
the surface lows swings towards northwestern Tennessee. However, very
meager moisture advection occurs on Saturday and a strong
temperature inversion is shown by models around 700 mb. These two
factors will likely keep shower activity very light and keep any
isolated thunderstorms from developing. As the surface low continues
to slide southeast Saturday night, the models try to break the cap.
They do not however really do this, but come close. If models do
break it though, there may be just enough moisture and good enough
low level lapse rates for a few strong storms capable of producing
some small hail, but for now left out of the forecast given the
strong cap and limited moisture expected. High chances of showers
look like a good bet though Saturday and Saturday night. It should be
fairly warm over the weekend with highs in the 60s to lower 70s and
lows in the upper 40s to mid 50s.

Models diverge quite a bit by Sunday into Sunday night concerning
how far south the cold front associated with the departed surface low
moves. Regardless though Sunday and Monday will be cooler. GFS does
not move it to the florida panhandle (like the ECMWF), but moves in
into southern/central AL, before lifting it further north late Monday
night as a warm front. If models are correct it should be a bit more
unstable as this warm front moves northeast through the area Sunday
night into Monday. Overall forecast atmospheric soundings do not look
very impressive. Some rumbles of thunder and brief heavy rainfall
may be possible with these storms, but not much else. Mainly
scattered showers and few thunderstorms (none too strong) look
possible Sunday night into Monday.

The next surface low and associated storm system develops over the
Rockies/Oklahoma on Sunday night into Monday morning. However, once
the warm front pushes north of the area by Tuesday evening, a drier
atmospheric profile returns, as upper level ridging builds into
Mississippi and Alabama. This strengthens on Tuesday, keeping a
strengthening storm system over Arkansas and Texas. This gives us a
break from precipitation Monday night through Tuesday. This period
could be a bit warmer than models are currently indicating, based on
ridging over the area. Overall models are similar, but do hold off
higher rain and possibly thunderstorms chances until Wednesday
afternoon evening of next week, given the strong upper level ridge
the system is trying to move into.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 615 AM CDT Wed Mar 21 2018

Clouds are lingering near KHSV as an upper system lifts east but
should stay few or sct for the rest of the morning. Another batch of
clouds are moving in from the northwest and may impact KMSL, maybe
KHSV, in the next few hours. Although they may go bkn or ovc, heights
will stay VFR. Both terminals should be seeing mostly clear skies by
the afternoon. Winds will also be gusty today out of the northwest.
They should increase quickly this morning with gusts around 30kts
possible by this afternoon. They will diminish with sunset
this evening.


AL...Freeze Warning from 2 AM to 8 AM CDT Thursday for ALZ001>010-016.

TN...Freeze Warning from 2 AM to 8 AM CDT Thursday for TNZ076-096-097.




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