Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 261437

Area Forecast Discussion
National Weather Service Huntsville AL
937 AM CDT Mon Jun 26 2017

.NEAR TERM...(Rest of Today)
Issued at 937 AM CDT Mon Jun 26 2017

A dry continental airmass prevails this morning across the TN Valley
while a shortwave trough axis (rotating around the parent longwave
trough) moving across TN/MO approaches. GOES 16 Visible satellite
data is already showing mostly mid-level clouds approaching NW
Alabama from W TN/N MS but these clouds are breaking before they
arrive. Light precipitation is also appearing on radar imagery across
north MS and western TN. However, regional current obs are showing
no precip measuring at the sites. This is consistent with the current
RAOBs and GOES 16 low-level WV sat imagery showing dry air
prevailing across MS/AL. So, am inclined to keep 10% POPs but keep
chance of precipitation out of the forecast. Did make some minor
adjustments to the sky cover forecast for those mid-level clouds
that are now arriving across NW AL.

Otherwise, trend updates were made to the air temperature, dewpoint
temperature, and wind forecast. May also need later adjustments to the
temperature forecast later if the mid-level clouds begin to affect
the daytime highs over NW AL.

.SHORT TERM...(Tonight through Wednesday night)
Issued at 302 AM CDT Mon Jun 26 2017

The shortwave mentioned above will drop out of the northern CONUS
towards the TN Valley late this evening into Tuesday morning. The
lift associated with the shortwave will be concentrated in the
700-500mb layer based of QG/omega analysis. This is also the region
where the moisture will be the highest. However, beneath the 700mb
layer forecast soundings continue to show a rather dry region where
dewpoint depressions are upwards of 20 degrees. So, while there is
more than enough lift and moisture to generate showers the question
is whether or not any of that rain will be able to reach the surface
and will any of the activity weaken as it drops SE as the models are
showing. Models have been decently consistent in showing some QPF
moving across the northern portions of the area with the shortwave.
Could see some type of thunderstorms complex develop over the
AR/NE/KS this afternoon and maintain its strength until it
approaches the MS River, then it would begin to fall apart. Now with
all of that in mind continued with the low PoP chances (<30 percent)
tonight through late Tuesday morning with highest chances in TN
closer to the vort max.

Clouds will be quick to clear out Tuesday as high pressure settles
into the area. The northerly flow and CAA should keep temps below
normal for another day with highs in the low to mid 80s. Tuesday
night into Wednesday will be a good radiational cooling night and
much of the area should see temps dip below the 60 degree mark. But
this will be the last "cool" night for awhile as winds quickly shift
to the south on Wednesday and moisture begins to stream back into the
area. Upper level heights increase Wednesday and with good WAA
occurring we can expect a warm-up in temps, afternoons highs
Wednesday should be in the upper 80s to around 90 degrees. Back to
normal for this time of year. Overnight temps Wednesday night into
Thursday will be about 10 degrees warmer compared to the previous
night with values in the upper 60s.

.LONG TERM...(Thursday through Sunday)
Issued at 302 AM CDT Mon Jun 26 2017

An upper-level ridge of high pressure centered across central
Florida will generally be the predominant synoptic feature in
control of the weather across the southeastern United States to
close out the work week. Generally, zonal flow will prevail aloft,
with the subtropical jetstream located to the north across the Great
Lakes/Ohio Valley region. This will result in a typical late June
warm/humid air mass, with the potential for some diurnally driven
convection during the afternoon/evening hours on Thursday/Friday.

The pattern will subtly change heading into the weekend, as the
aforementioned high shifts east into the Bahamas. An upper-trough
will drive southeastward from the Canadian prairies into the
Northern Plains and Great Lakes region by Saturday. This, in turn,
will drive a weak cold front into the Ohio/Mid-Mississippi Valley
and result in some increased shower and thunderstorm activity along
and ahead of this boundary (thanks to weak shortwave rotating around
the base of the trough), in a fairly moist and moderately unstable
air mass. Though shear parameters will be fairly weak, ML Cape values
are progged to be in the 1500-2000 J/kg range by Saturday and Sunday
-- resulting in scattered to perhaps widespread strong convection
through the afternoon/evening. Damaging winds due to a localized
downburst would be the primary threat with this activity. Given the
lower shear values, this convection will be slow and fairly
unorganized. With PWATs progged to be as high as 1.9 inches in this
humid air mass, a locally heavy rainfall/flooding threat with the
slow-moving, stronger cells is possible.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 624 AM CDT Mon Jun 26 2017

VFR conditions are forecast for the TAF period. A SCT deck of mid-
level clouds will arrive into the area later this morning. A system
moving through the Midwest will keep these clouds in place and could
result in a few showers approaching the area towards the end of the
TAF period. Confidence in rain actually making it into the terminals
is low and will keep it out of the forecast. Winds will favor a N/NW
direction with speeds at or below 10 kts.





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