Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Memphis Tennessee
1240 PM CDT Wednesday Aug 20 2014

Update...
update for 18z tafs

&&

Previous discussion... /issued 1045 am CDT Wednesday Aug 20 2014/

Update...
temperatures are running generally 4-6 degrees above where they
were yesterday. Yesterdays highs were generally in the low
90s...pure extrapolation would put todays highs in the middle to
upper 90s...generally within a degree or so our current forecast
highs. Dew points remain in the middle 70s. The 100 dollar
question is how much atmospheric mixing we will see this
afternoon. Dew points just off the surface drop off very
quickly...into the middle 60s only a couple thousand feet above
the surface. Only 2-4 degree lower relative humidity will make a
big difference in our afternoon heat indices. A heat advisory
is in effect for heat indices at or above 105 degrees for most of
the midsouth. Today will likely be The Bench mark setting the
groundwork for the basis for a need for additional advisories
during the remainder of the week.

Previous discussion... /issued 744 am CDT Wednesday Aug 20 2014/

Discussion...water vapor satellite trends along with 00z upper
air analysis indicates an upper level ridge axis centered across
the Southern Plains and portions of the lower Mississippi Valley
early this morning. A few high clouds are moving across portions
of Arkansas this morning with mainly clear skies prevailing at
this point. As of 4 am CDT...temperatures are still quite warm in
the middle 70s to around 80 degrees with the warmest temperatures
near the Mississippi River. Very hot and humid conditions for
today and persisting into the upcoming weekend will be the
predominant concern in this morning/S forecast issuance.

An upper level ridge located over the Southern Plains and western
sections of the lower Mississippi Valley will gradually build east
across the middle south today and strengthen across the lower
Mississippi Valley Thursday through the upcoming weekend. Surface
dewpoints this morning remain quite high in the middle 70s across
many locations early this morning. 925 mb temperatures are
expected to increase to 26-27c...translating to afternoon highs in
the middle to upper 90s. Very hot temperatures combined with the
anticipation of surface dewpoints only mixing out to the lower 70s
suggests heat index readings may average between 105 to 108
degrees across much of the middle south with the exception being
portions of northeast Mississippi and west Tennessee near the
Tennessee River. Consequently...I have issued a heat advisory
between 11 am CDT and 7 PM CDT for much of the middle south.

These very hot conditions are expected to persist Thursday and
into the upcoming weekend. Afternoon high temperatures in the
upper 90s to approaching 100 degrees and very high surface
dewpoints may result in heat index readings at or above 105
degrees during this period with overnight lows in the middle to
upper 70s. Later shifts will continue to monitor trends and extend
the duration and coverage of the heat advisory if conditions warrant.

Afternoon high temperatures may cool slightly next week as latest
00z GFS/European model (ecmwf) long term models indicate a potential for increasing
low level moisture across the lower Mississippi Valley due to tropical
moisture from the Gulf of Mexico. This may also result in isolated
showers and thunderstorms especially during the afternoon and
early evening hours next week.

Cjc

&&

Aviation...
18z taf cycle

VFR conditions expected through forecast period with exceptions from
08z-14z at mkl due to fog formation under clear skies and light
winds and possibly at tup for the same reason.

Belles

&&

Meg watches/warnings/advisories...
Arkansas...heat advisory until 7 PM CDT this evening for Clay-Craighead-
Crittenden-cross-Greene-Lawrence-Lee Arkansas-Mississippi-
Phillips-Poinsett-Randolph-St. Francis.

MO...heat advisory until 7 PM CDT this evening for Dunklin-Pemiscot.

MS...heat advisory until 7 PM CDT this evening for Benton MS-Calhoun-
Chickasaw-Coahoma-DeSoto-Itawamba-Lafayette-Lee MS-Marshall-
Monroe-Panola-Pontotoc-Quitman-Tallahatchie-Tate-Tunica-
Union-Yalobusha.

Tennessee...heat advisory until 7 PM CDT this evening for Crockett-Dyer-
Fayette-Gibson-Haywood-Lake-Lauderdale-Obion-Shelby-Tipton-
Weakley.

&&

$$

National Weather Service Glossary of Abbreviations