Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
320 am CDT Tuesday Aug 4 2015

issued at 320 am CDT Tuesday Aug 4 2015

Gorgeous early morning in progress with comfortably cool
temperatures... light winds and mainly clear skies all compliments of
sprawling ridge of high pressure from the upper Midwest through
the Ohio Valley. Temperatures at 2 am ranged from the middle 50s in the
valleys and favored drainage locations north to the lower 60s
south... roughly some 5-10 degrees below normal. Regional radar
imagery shows convection extending from portions of South Dakota through
eastern NE...far southwest Iowa and northern MO along 850 mb
convergence axis with aid of weak disturbances propagating down
in northwest flow aloft. Additional convection was noted
sliding southeastward into portions of Southern Plains ahead of shortwave
trough. Main feature of note is stronger shortwave over Wyoming
early this am. This system will emerge into the plains later today
then slide east/southeast passing mainly south of the area later Wednesday... but
close proximity for rain chances developing across the southern
County Warning Area.


Short term...(today and tonight)
issued at 320 am CDT Tuesday Aug 4 2015

Another great Summer day is on tap for the region as high pressure
slowly traverses the area... providing near to slightly below
normal temperatures with highs around 80 or lower 80s and low humidity.
Winds to be lighter today with the high overhead. Otherwise much of
the area sunny to mostly sunny with just some thin cirrus.
Exception will be far southern sections where may see periods of
thicker cirrus and possibly middle clouds being in closer proximity
to the convection. Did keep some small probability of precipitation far southwest County Warning Area
for mainly later today... but overall isentropic lift on 320k surface
and elevated convergence zone while drifting eastward a bit later
today (as ridging begins to slide east) remains focused to our west
and south.

Tonight...slowly spread lower chance probability of precipitation northward with some
lifting northward of weak isentropic lift and elevated convergence
zone... with precipitation chances mainly south of Cid to mli. Otherwise...
generally another pleasant night with lows coolest north/northeast
(50s) where skies mainly clear and drier low level air while
warmer south (60-65) due to clouds and some uptick in moisture.

Long term...(wednesday through monday)
issued at 320 am CDT Tuesday Aug 4 2015

Main forecast concerns for the long term are a low and vorticity maximum that
moves to the south of the area in the beginning of the period and
the sustained northwest flow and the waves transversing the flow.
Currently it looks as though the next couple of days will be dry
with the exception of the southern County Warning Area. Later in the
period...substantial differences between guidance remain at the end
of the a result....superblend has slights to chance probability of precipitation
through the extended.

Wednesday through Thursday am...

Large amplitude ridge to our northwest will continue to push drier
air into the area along with surface high pressure over the Great Lakes.
This will inevitably keep the surface flow out of the east. A decent
shortwave trough is transversing below the high amplitude ridge across
the NE Panhandle tonight. After this time the models differ in
solutions. The GFS seems to be the most unreasonable as it tries to
force the wave headstrong into the northwest flow and then dive south.
This solution produces decent precipitation for our area. I believe this
is wrong and that the 12z and 00z European model (ecmwf) has a much better handle on
this storm. The wave should interact with the northwest flow and dive
south. This will keep cyclogenesis and the overall precipitation mainly
south of i80 with the best chances being south of Highway 34. 12z wpc
guidance also supports this notion. As a result of this and the
easterly flow...the elevated warm front will struggle to move into
the area before it is ushered quickly to the south and the east.
North of the area...another wave moves through the flow. This wave
will also produce precipitation...but keep most of it north of the area
if not completely out of area. If you are looking for rain...this
is not a good week so far.

Thursday PM and later...

Yet another wave in the flow is forecast to move across southern Canada.
This wave appears to be more robust and will lead to cyclogenesis to
our north. The low and attendant boundaries should move through
the area Friday. The best chance for probability of precipitation will be across northern
zones as the better convergence will be across the area. The GFS
develops a second surface low....this seems unreasonable. After this
period northwest flow becomes entrenched across the area again and will
likely lead to more waves in the flow. There are differences in the
model solutions last night...leads to schc to low chance
probability of precipitation through the rest of the extended.


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1045 PM CDT Monday Aug 3 2015

VFR conds through this taf cycle as weak high pressure builds into
the area. Any showers will remain in MO closer to a stalled frontal
boundary there. Mainly northwest to west winds less than 10 knots
through the period.


Dvn watches/warnings/advisories...


short term...m^2
long term...Gibbs

National Weather Service Glossary of Abbreviations