Area Forecast Discussion
Issued by NWS Huntsville, AL

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083
FXUS64 KHUN 271025
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
525 AM CDT FRI MAY 27 2016

.DISCUSSION...
Latest analysis of upper-air observational data and short term model
guidance suggests that the local area remains beneath the crest of
a 500-mb ridge axis extending northward from subtropical high located
across central Mexico. To the west of the region, stronger
southwesterly gradient flow exists between the ridge and a mid-level
shortwave trough across eastern CO/western KS. The combination of
deeper moisture and enhanced lift from several lower amplitude waves
ejecting nnewd from southeast TX into the lower Great Lakes continues
to result in widespread rain/thunderstorms across much of the
Mississippi Valley -- but with little eastward progression into
northern AL/southern TN.

To the east of the region, another subtropical ridge extends from the
Outer Banks toward Bermuda -- with a weak mid/upper-level low
centered across the Bahamas. The development of nocturnal convection
across GA/SC has likely been enhanced by the remnants of a weak mid-
level trough which brought rainfall to east TN last night, and
stalled in increasingly diffluent flow east of the southern
Appalachians.

Short term guidance is in general agreement that the residual mid-
level wave/shear axis to the east of the region will drift slowly
southwestward today as the Bahamas upper low lifts northwestward.
This feature -- along with increasingly diffluent flow aloft -- will
provide a slightly more favorable environment for the development of
late morning/afternoon convection across northeast AL, with moderate
south-southeasterly steering flow allowing this activity to shift
nwwd through the late afternoon/early evening before dissipating. As
the ridge aloft continues to weaken overnight...another disturbance
in southwest flow may bring a separate round of rain/storms to the
region early Saturday morning, before lifting northeast of the region
during the afternoon. Although PWAT values rising into the 1.4-1.6
inch range will support a greater coverage of precip than what we
have seen the last few days, overall nature of lift appears to be too
weak to justify greater than a 30-40% POP. Given very weak deep-layer
shear and forecast MLCAPE in the 500-1000 J/kg range, brief gusty
winds and lightning will be the main threats with any storms that
develop. Cloud cover will have a more significant impact on temps,
with highs likely only reaching the m/u 80s today and Saturday.

By the second half of the weekend, a stronger shortwave trough over
the central Plains is forecast to eject northeastward into the
Upper Mississippi valley/western Great Lakes, with remnants of weak
shear axis over our region becoming absorbed in circulation around
cyclone approaching the coast of SC. A mid-level ridge axis will
amplify across the region Sunday in response to this -- suppressing
the threat for convection and allowing temps to rise well into the
lower 90s once again.

In the extended forecast period, medium range guidance from the
GFS/GEM/ECMWF all suggest that the southeastern CONUS low will open
into a wave and lift very slowly northward across the Carolinas and
into VA during the first half of next week. Although the the region
will remain under the influence of mid-level ridging on Memorial Day,
strong boundary layer heating should be sufficient for the
development of isolated afternoon thunderstorms as temps rise into
the lower/mid 90s. The ridge aloft will begin to translate eastward
Tuesday, with a southwest flow aloft expected to prevail for
remainder of the forecast period. A gradual increase in both deep-
layer moisture and lift in this regime may provide for a subtle
increase in the coverage of afternoon/early evening showers and
storms from Tuesday-Thursday. However, there are indications that the
Atlantic subtropical ridge may build westward across the southeastern
CONUS late in the forecast period, and this would warrant lower POPs
and even higher temps than currently advertised late next week.

70/DD

&&

.AVIATION...
(Issued 1151 PM CDT THU MAY 26 2016)
For 06Z TAFs:

VFR conditions will prevail through the next 24 hours at the KMSL and
KHSV terminals. Winds will generally remain from the south and may
gust at times during the afternoon, however confidence is too low to
add gusts in the forecast.

73

&&

.PRELIMINARY POINT TEMPS/POPS...
Huntsville    89  68  86  65 /  20  40  40  20
Shoals        89  68  87  64 /  20  40  40  20
Vinemont      86  66  85  63 /  20  40  40  20
Fayetteville  87  66  83  62 /  20  40  40  20
Albertville   86  65  85  62 /  30  40  40  20
Fort Payne    85  64  85  61 /  30  40  40  20

&&

.HUN Watches/Warnings/Advisories...
AL...NONE.
TN...NONE.
&&

$$

For more information please visit our website
at weather.gov/huntsville.



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