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Area forecast discussion 
National Weather Service Huntsville Alabama
645 am CDT Sat Jul 26 2014

Update...
for 12z tafs

&&

Discussion...
/issued 233 am CDT Sat Jul 26 2014/
water vapor and model analysis indicates a large upper level
anticyclone over the southern Continental U.S.. a potent upper low was
positioned to its north over Saskatchewan with a jet core in between
from the northern rockies through the Great Lakes and Ohio Valley.

Hot weather is expected today and Sunday, with increasing moisture
owing to heat index values of 100-105f. We split the difference on
the MOS temperatures (gfs has been typically too warm), but the advection
of 850mb temperatures in the l-m20s make readings in the l-m90s seem very
plausible. Forecast soundings indicate a formidable capping inversion
today, so few clouds are expected. Dew points of near or just above
70f will return on Sunday as persistent S-southwesterly flow occurs. The cap
may yet be strong enough to prevent deep convection, but will keep
isolated T as a possibility during the late afternoon. If the cap can
break, instability/cape and a drier 8-500 mb layer would support
downburst activity.

The cold front arrives Sunday evening in southern Tennessee. Robust
convective activity looks to be ongoing along the front over eastern
Tennessee which should tend to back-build westward into the favorable 25-35kt
low level inflow (9-800 mb levels) and Theta-E ridge posn. The capping
inversion will likely hold development back until this occurs. The
cap also lends to lower confidence as to areal coverage of storms
Sunday night. Middle level northwesterly flow of 30-35kt will increase effective
bulk shear values, but not certain if this will be sufficient for a
supercell storm Mode vs multi-cell clusters as upper level winds
remain relatively weak. The Storm Prediction Center outlook emphasizing areas to our NE
looks good, but a couple of severe storms may occur in our area
Sunday night as well.

As has been advertised, the medium range models continue to take the
upper low southeast into the a deeper trough position by early next week over
the eastern Continental U.S. While the ridge retrogrades westward a across The
Rockies/southwestern Continental U.S.. this will bring another welcome period of below
average temperatures and lower humidity through the middle to end of next week.

Alaska

&&

Aviation...
for 12z tafs...patchy br/fog currently being reported at both hsv/mean sea level
will gradually lift through 26/14z...but will also require initial
tempo for MVFR visibility reductions to 3 sm. Otherwise...VFR conds are
expected to persist with development of few cumulus around 3500 feet by late
morning and increasing Alto/cirroform clouds by middle to late afternoon. A
strengthening westerly low-level jet late tonight may support a lower deck
of stratus between 27/09-12z but did not include with this taf issuance.
A complex of thunderstorms and rain may also shift southeastward into eastern Tennessee by end of taf
period...but should remain well displaced to the North/East of both
terminals. Surface winds will remain from the SW at speeds of 5-10 kts.

70/dd

&&

Hun watches/warnings/advisories...

Alabama...none.

Tennessee...none.

&&

$$

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