Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
606 PM EDT Wednesday Aug 20 2014

Synopsis...
issued at 605 PM EDT Wednesday Aug 20 2014

Periodic showers and thunderstorms are possible tonight into
Friday as a warm front slowly moves north into the area. Heat and
humidiity will return by Friday as this front moves north. Lows
tonight will be in the 60s with highs on Thursday in the low 80s.

&&

Short term...(this evening through thursday)
issued at 251 PM EDT Wednesday Aug 20 2014

Tranquil afternoon so far in shallow Post frontal airmass. However ll drying
has not been as extensive as indicated in prior model solutions and
isolated rain showers northwest shld uptick some through this afternoon given band of
aggravated cumulus across extending eastward into Northwest Ohio.

Otrws primary difficulty is west/northward rtn of surface frontal zone inadv of next
SW disturbance rolling eastward through southwestern Canada this afternoon. While
model guidance is similar aloft...timing of strong ll moisture flux
differs and generally sided west/slwr solutions in light of current
complex working through southeast Illinois/SW in...thus slowed arrival of
likely probability of precipitation SW half until 12z. Active wmfntl zone expected to continue
on Thursday especially central/west under the Assumption that outflw/warm front
composite anchors surface frontal zone through northern in if not further
south. Bumped southwestern half higher yet cut far NE lower per consensus of
highres guidance. Prior temperatures likely too warm as noted in upstream
temperatures under extensive clouds/precipitation this afternoon and have cut maximum temperatures
some but likely not enough SW. Will let night shift take another
look at that.

&&

Long term...(thursday night through wednesday)
issued at 251 PM EDT Wednesday Aug 20 2014

Warm front will continue to slowly lift northeast Thursday night
into Friday. Suspect an mesoscale convective system will develop somewhere over the upper
Midwest Thursday night with low level jet strengthening to around 30-40 kts
and strong Theta-E advection. This mesoscale convective system will eventually dive
southeast early Friday morning. Low confidence in exact track of
nocturnal convection but it could impact our County Warning Area. This combined with
potential for lingering convection from the afternoon supports at
least a high chance pop for Thursday night. There is a low chance of
severe weather into the overnight period with forecast soundings
indicating around 1000 j/kg of elevated instability. Heavy rain may
be the bigger threat with precipitable water values at or above 2 inches and
potential for training storms.

Uncertainty remains unusually high for precipitation chances Friday into
the weekend. Warm front will likely stall somewhere over the Great
Lakes and wash out a bit. 12z nwp suite continues to show widespread
convective quantitative precipitation forecast but forecast soundings also show a decent warm nose
around 850mb. Combined with a lack of forcing mechanism amid
building longwave ridge...suspect model quantitative precipitation forecast may be overdone.
Maintained just a low chance Friday into Saturday. Kept Sunday and
Monday dry though an isolated storm cant be completely ruled
out...especially in our northeast counties where the cap will be
weaker. Midlevel trough and surface cold front will eventually
arrive with a better chance of rain but latest models now suggest
that could be as late as Wednesday.

Somewhat higher confidence aspect of the forecast will be the heat
and humidity over the weekend. 850mb temperatures still look to be around
20c and most guidance agrees on high temperatures around 90f. Surface
dewpoints also expected to hover in the low to middle 70s...supporting
heat index values near 100f in our southern counties.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 145 PM EDT Wednesday Aug 20 2014

VFR conds to begin the period in shallow Post frontal airmass behind
departing SW disturbance lifting out through southeastern Ontario. However
upstream SW over southern British Columbia will carry eastward overnight and aide northward rtn of
wmfntl boundary back across the middle MS valley. Expect storms will fire in vicinity of
of terminals toward 12z west/thunderstorms and rain probable Thursday am west/period of MVFR conds possible.



&&

Iwx watches/warnings/advisories...
in...none.
Michigan...none.
Ohio...none.
Lm...none.
&&

$$

Synopsis...ceo
short term...T
long term...agd
aviation...T



Visit US at www.Weather.Gov/iwx (all lower case)

Follow US on facebook...twitter...and youtube at:
www.Facebook.Com/nwsnorthernindiana
www.Twitter.Com/nwsiwx
www.Youtube.Com/nwsnorthernindiana

National Weather Service Glossary of Abbreviations