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Area forecast discussion 
National Weather Service Huntsville Alabama
238 am CDT Friday Aug 28 2015

Discussion...

An unseasonably cool and dry air mass will abate later tonight as
the southern flank of an exiting trough off the East Coast becomes
cutoff from the prevailing westerlies. Currently this upper low is
located over the north central Gulf Coast. Over the course of today
and tonight, it will gradually begin to affect the prevailing low to
middle level flow acting to slowly saturate the middle levels. Though
saturation will not occur rapidly enough to result in storm
development, low level cloud cover advecting from the east should
develop this afternoon. An additional impact will be the wind
direction shift to easterly to southeasterly for low-middle levels.
This change in wind direction will act to increase moisture
advection from both the Gulf of Mexico and Atlantic. So that by
Saturday, saturation is anticipated through much of the vertical
column, which combined with the approaching cutoff low will increase
chances for precipitation. A look at forecast soundings and plan
view representation of instability show steep low to middle level lapse
rates with low to moderate conditional instability on Saturday and
again on Sunday. As a result, thunderstorm development is forecast,
but without appreciable wind shear, any thunderstorms that do occur
to be pulse-like in nature. Due to the model run consistency, will
raise pops, especially for the afternoons on both Saturday and
Sunday. On the temperature front, with the Tennessee Valley back in a
maritime tropical environment on both days, expecting daytime high
temperatures to rise close to 90 with a higher probability for
breaks in the clouds over the western half of the County Warning Area to contribute
to these highs.

Then, by Sunday, the cutoff low appears to begin shifting northeast
towards the eastern Appalachians (merging with an approaching
shortwave trough) resulting in a decrease in shower/storm activity.
Because of its prognosticated exit, have tapered probability of precipitation to mainly NE Alabama/S
middle Tennessee on Monday. A sheared trough then forms on the southern
flank of the approaching shortwave trough over mi/IL/in. This
portion of the shortwave trough may act as a focus for thunderstorm
activity by Wednesday, but due to the uncertainty with this and the
track of tc Erika, if it survives, will keep low probability of precipitation mainly for
Wednesday. There is pretty low confidence in the forecast due to the
interactions with this sheared trough and possible direct/indirect
impacts from tc Erika. Furthermore, will keep temperatures near or
just below average (30 year) for this time of year on Monday and
Tuesday (daytime highs near 90s and overnight lows in upper 60s).
However, with the increase in surface dewpoints (i.E. Return of Summer
like humidity), expect it to feel warmer with heat index values
returning to the low to middle 90s by middle week.

Sl.77

&&

Aviation...
/issued 1146 PM CDT Thursday Aug 27 2015/
for 06z tafs...with high pressure to the NE continuing to impact the
weather across the region...VFR conds are xpcted through the taf period.
Only exception may be some brief -br near the kmsl terminal during
the early morning hours...although the probability is not high enough to
include in the forecast at this time. Scattered middle clouds should also once again
develop during the late morning/early afternoon hours in response to
daytime heating.

09

&&

Preliminary point temps/pops...
Huntsville 88 68 85 68 / 0 0 30 30
Shoals 89 68 86 68 / 0 0 20 20
Vinemont 87 68 83 68 / 0 0 30 30
Fayetteville 88 67 83 67 / 0 0 30 30
Albertville 88 68 82 68 / 10 10 40 30
Fort Payne 88 67 82 67 / 10 10 40 40

&&

Hun watches/warnings/advisories...
Alabama...none.
Tennessee...none.
&&

$$

For more information please visit our website
at weather.Gov/Huntsville.

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