Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
626 PM CDT Thursday Jul 10 2014

Update...
issued at 622 PM CDT Thursday Jul 10 2014

I have updated tonight and Friday to reflect a drier forecast.
This is due to a weak and westward position of the low level jet
tonight...and therefore a less likely propagation of any
convection into the County Warning Area during the late night and morning. A mesoscale convective system
still appears likely Friday night...and have focused all forecast
products on this as the main onset of rainfall.
Ervin

&&

Synopsis...
issued at 330 PM CDT Thursday Jul 10 2014

High pressure has shifted to the Great Lakes bringing a return to
southerly winds to the County Warning Area but still plenty of sunshine. Dewpoints
have crept up to around 60 at most locations with 3 PM temperatures
in the upper 70s to lower 80s.

Elsewhere...warm air advection was strengthening in the plains with
a rather large shield of middle/high clouds in the northern plains.
This was ahead of an impressive upper low seen on water vapor movie
loops in the Alberta/Saskatchewan provinces of Canada. Current
temperatures under this low are only in the 50s and 60s.

&&

Short term...(this evening through friday)
issued at 330 PM CDT Thursday Jul 10 2014

Forecast focus on thunderstorm chances late tonight and Friday.

Tonight...warm air advection clouds will increase especially after
midnight as the low level jet continues to strengthen in the
plains. Late tonight this jet veers into the dvn County Warning Area but the
better forcing is suggested to remain west of the County Warning Area. However...will
mention a small chance for any thunderstorms that may spill into
our far western counties well after midnight. Minimum temperatures
will range from the upper 50s NE to the middle 60s SW.

Friday...operational models not as bullish on rain compared to the
past several runs. Therefore...have reduced probability of precipitation to high end chance
instead of likely. This is due to the better forcing remaining
west of the County Warning Area but still enough to warrant probability of precipitation. Will follow the
European model (ecmwf) which is the Leader in verification the past 3 months according
to wpc. Expecting plenty of middle/high level clouds but still enough
breaks to push temperatures into the upper 70s north to 80 to 85 south.

Long term...(friday night through thursday)
issued at 330 PM CDT Thursday Jul 10 2014

Active period this weekend to be followed by unseasonably cool
conditions next week as an upper low originating in northern Canada
is expected to drop down over the Great Lakes.

Friday night through Saturday night will have a threat of locally
heavy rainfall as a series of mesoscale convective system/S affect the region. Precipitable
water forecasts...model quantitative precipitation forecast and wpc days 1-2 quantitative precipitation forecast forecasts suggest 1
to possibly 2 inch totals possible mainly north of I-80 through
Saturday night. The first thunderstorm complex will likely set up
over central Iowa into east central Iowa late Friday evening as a
southwesterly low level jet and strong thetae advection interact
with a shortwave in the middle level westerly flow. This mesoscale convective system would
track east through the forecast area overnight...laying out a west
to east boundary that would act as a focus for daytime convection
with the next triggering shortwave Saturday afternoon. Our likely
probability of precipitation follow this scenario. There will be a potential for severe
convection as shear profiles become more supportive for possible
damaging wind and...to a lesser extent...large hail with the
strongest storms in the Saturday afternoon and evening hours.
Current model timing suggests this would track east out of west central
and northwest Illinois Saturday night. Dewpoints and overnight mins will return
to the upper 60s to lower 70s with highs back into the lower to middle
80s.

Sunday into Sunday night...thunderstorm chances will continue as a
cyclonic upper level flow with embedded impulses builds southward
over the region. However...at the 850 mb level...the flow becomes
weaker and more west to northwesterly...suggesting more organized
thunderstorm complexes will focus along the main convergence axis
over the far south...or just south of the forecast area. Just where
the associated surface boundary hangs up will be critical for
rainfall potential and coverage...which at this time is more favored
over or south of southeast Iowa into west central Illinois. This would
hopefully be a shift in the axis under the gun for locally heavy
rainfall southward from the previous 36 hours.

Next week...the strong upper low moving over the Great Lakes and
associated Canadian high that builds into the central U.S. Will
bring dry and unseasonably cool conditions Tuesday through Thursday.
Highs Tuesday may struggle to climb out of the 60s over especially
the north...which should then moderate back into the 70s Wednesday and
Thursday. Overnight lows in the 50s will be common throughout with a few
upper 40s not out of the question Tuesday night and Wednesday night.

&&

Aviation...(for the 00z tafs through 00z Friday evening)
issued at 622 PM CDT Thursday Jul 10 2014

VFR weather will continue overnight...as high clouds gradually
increase over the region. A mainly dry day is expected
Friday...with isolated thunderstorms possible towards afternoon.
Thus...dry tafs and VFR weather will continue through 00z/12.
Winds will be southeast around 8 kts tonight...then increase to 10
to 14 kts Friday...also from the south to southeast.
Ervin

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Update...Ervin
synopsis...haase
short term...haase
long term...sheets
aviation...Ervin

National Weather Service Glossary of Abbreviations