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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1235 PM CDT Friday Sep 19 2014

issued at 320 am CDT Friday Sep 19 2014

Stratus/patchy fog was located across northwest Illinois with visibility at
Freeport Illinois down to 1 mile at 300 am. This area of stratus began
late yesterday afternoon coming off of Lake Michigan in southeast WI and
has been expanding southwest ever since. Strong moisture transport/
Theta-E advection was occurring in the Dakotas and into northern
Minnesota where middle/high level clouds were spreading southeast. There was
also a cluster of thunderstorms in far northern South Dakota.

At 3 am temperatures across the dvn County Warning Area were in the lower to middle
50s but were in the mild 60s to around 70 in the Dakotas southward
into Texas.


Short term...(today and tonight)
issued at 320 am CDT Friday Sep 19 2014

Forecast focus on thunderstorm chances late tonight.

Today...stratus/patchy dense fog will dissipate by middle morning as
southerly winds increase and mix out the stratus/fog. Otherwise
the better forcing will remain to our northwest with mainly cirrus
spilling into portions of the County Warning Area. South winds will also push
warmer temperatures into the area with afternoon highs in the middle
to upper 70s. Low pressure pushing across the upper Midwest will
tighten the gradient over our northern County Warning Area with south winds gusting
to 25 to 30 miles per hour...especially this afternoon.

Tonight...low pressure will be tracking into the northern Great
Lakes sending a cold front southeast into far northern Iowa towards
morning. There will be a chance of thunderstorms ahead of this
front and I will continue the small probability of precipitation in our far north late tonight.
Low level convergence/forcing will be weakening and instability
will be at a minimum so rainfall should be light. South to southwest
winds will keep temperatures mild the lower 60s at most

Long term...(saturday through thursday)
issued at 320 am CDT Friday Sep 19 2014

Possible showers and storms on Saturday with frontal passage...then
dry conditions and near normal temperatures.

Long term forecast confidence assessment...above average or good
with typical uncertainties of coverage and any precipitation
amounts on Saturday. Also is the risk...if any...of strong to
severe storms Saturday PM. Minor sensible weather issues after
Saturday with splendid early Fall weather.

Overview...initialization and verification very good with minor
sensible weather issues noted forecast by all solutions. Verification
and run to run analysis supports a blend of all solutions with
diurnal temperature ranges possibly a bit underdone most days with
highs a degree or two higher and lows at least a degree or two

Saturday...minor changes to forecast with 20 to 50 percent probability of precipitation as
front passes with modest forcing and shear that suggest low risk...
if any of severe storms in PM hours with front. SBCAPE adjusting
for bl moisture biases suggest 2000-2500 j/kg and wbz of 12+k above ground level
and 850-700mb winds of 25-30 kts appears reasonable with frontal
passage. Some isolated strong storms appears most plausible with
these parameters of small hail up to pennies and gusty downdraft
winds of 35 to 45+ miles per hour per local tools and techniques. Rain totals
generally light with isolated moderate amounts of .25 to .75 inches
in any storms suggested. Highs in the lower 80s most locations under
a partly sunny sky and upper 60 dewpoints for a warm day but south
winds of 10 to 20 miles per hour make for a decent early fall day if outside.

Saturday night...removed probability of precipitation but far southeast 1/4 with slight chance there
in the evening as front passes and drier air moves in. Skies should
clear by late evening with northwest winds of 5 to 15 miles per hour. Lows in far northwest
sections may need trimming a degree or two if drier air moves in
faster down to near 50 to near 60 degrees in far southeast sections.

Sunday and Sunday night...fair skies and cooler with northwest winds of 10
to 20+ miles per hour and highs mostly 70 to 75 degrees for a breezy but
otherwise near ideal early fall day. Sunday night...seasonably cool
with lows mostly 45 to 50 degrees with favored low lying locations
north sections possibly still a degree or two too mild for later
shifts to consider.

Monday though Thursday...quiet early Fall weather with fair skies
under large high pressure system and light winds and highs mostly
70-75 through Wednesday...then 75-80 on Thursday as south winds
develop. Mins around 50 degrees rising into the middle 50s by
Thursday and Friday morning.


Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1231 PM CDT Friday Sep 19 2014

VFR conditions will be seen through 06z/20 as high pressure moves
to the East Coast. After 06z/20 a front in the upper Midwest and
plains begins moving toward the area. Some nocturnal convection is
expected so vcsh was included in the 18z tafs. If a rain showers or an
extremely isolated thunderstorms and rain would affect a taf site...a brief period
of MVFR conditions would be possible.


Dvn watches/warnings/advisories...


short term...haase
long term...Nichols

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