Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
1251 PM EDT Friday Jul 25 2014
issued at 435 am EDT Friday Jul 25 2014
High pressure over the southern Great Lakes will drop southeast to
the middle Atlantic region by tonight. This will allow for a chance
of showers and storms to progress from the upper Midwest into the
area tonight. Highs today will be just a bit below normal...
primarily in the upper 70s to around 80. Lows tonight will
generally be in the lower to middle 60s.
Short term...(today and tonight)
issued at 434 am EDT Friday Jul 25 2014
Central/eastern Iowa complex this am to likely dive southeast along
low level Theta-E gradient...keeping chances today relegated well
southwest of County Warning Area. Dropped any mention today as low level moisture
recovery to remain staid.
Focus on better potential for elevated convective complex arrival
late tonight. Temporarily rexed intense northern stream wave
centered this am across southeastern Alberta to overtop subtropical ridge
and unleash southeastward whilst phasing into southern extension of northern
Quebec longwave trough through dys2/3. While initially southern
lobe/extension of middle tropospheric height falls minor amid last
vestiges of leading low amplitude ridge...it appears that vigorous
upstream kinematic profile and ample MUCAPE pool of 2000-3500 j/kg
through i94 to i80 corridor over upstream/upper Midwest on eastern
periphery of advancing eml should be quite favorable to convective
complex production by late this evening. Additionally...favorable
upper level exit region of jet should aim to maintain elevated
convective progression into County Warning Area...especially toward daybreak.
Explicit mesoscale temporal/spatial details with respect to convective complex
initiation still a bit dubious...lending overall conditionality to
coverage/timing and kept mention no higher than high chance at this time with
northwest to southeast gradient.
Long term...(saturday through thursday)
issued at 434 am EDT Friday Jul 25 2014
A warm front will lift northeast ahead of a surface low by early
Saturday morning. 850 mb temperatures should rise to near 20c by late
tonight per GFS and European model (ecmwf). Initial morning convection should be
mainly over favored areas of low level Theta-E flux/convergence...so
have reoriented shower/storm chances to coincide with this area of
convergence with highs rain chances over east areas. However...later
in the day...the airmass will become extremely unstable with convective available potential energy
near 4000 j/kg near klaf. Some sref members have values as high as
4500 to 5000 j/kg. Have raised storm chances late in the day with
this great instability where low level moisture flux will be
increasing. The best chance for severe storms appears to be in the
evening and overnight Saturday night as the larger scale assent
favors these strong storms and as wind shear becomes more favorable.
BUFKIT/NAM at laf has sweat indices rising to around 500. An upper
level trough will move across the area late Sunday/Sunday night with a
continued chance for more showers and storms. Much cooler air will
move into the area early in the work week with highs in the 70s.
Kept the forecast dry.
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1251 PM EDT Friday Jul 25 2014
Mainly VFR through the forecast period with slow top down
moistening occurring in advance of an approaching warm front. Weak
shortwave dropping southeast out of Wisconsin in tandem with
initial 700 mb Theta-E surge may be enough to allow a few
sprinkles/light showers to reach mainly ksbn by late this
afternoon/evening. Otherwise...no changes beyond this evening
given low predictability/confidence for elevated convection to
impact the terminals late tonight/Saturday morning on the leading
edge of eastward advancing eml/elevated instability pool.
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