Area forecast discussion
National Weather Service quadrant cities Iowa Illinois
633 PM CDT Thursday may 23 2013
Synopsis...
issued at 216 PM CDT Thursday may 23 2013
Latest surface analysis was indicating large Canadian ridge nosing
down across the upper Midwest with associated pressure rise maximum
fields still occupying much of the local County Warning Area and into the
southwestern Great Lakes. Cumulus/stratocu fields across the County Warning Area hanging on
some and even reforming in areas of earlier clearing...but
flattening rising trends also noted and incoming drying/subsidence
fields seen on water vapor imagery will win out into the evening.
Aloft...W/v imagery also indicating l/west trough taking shape across the
western Great Lakes while Omega upper ridge gets squeezed across the
northern plains and west central Canada.
&&
Short term...(this evening through friday)
issued at 216 PM CDT Thursday may 23 2013
Tonight...incoming ridge to continue to bring along with it clearing
subsidence this evening...while surface winds decrease and try to decouple
into early Friday morning. Incoming cool advected air mass and drying
surface dewpoints support widespread lows from 40-45 degrees...but the
northeastern third of the dvn County Warning Area may look to cool into the upper
30s like what is already advertised. 850 mb mb ridge cold rule even
supports some middle 30s in those areas which could mean patchy
frost. But came up with lows similar to what is advertised and
will not change much what is ongoing...thus will not mention frost
and lows few degrees above record levels. Hopefully will just be a
heavy dew. Will not mention fog as well with dry surface dpt
influx...but some River Valley fog will probably occur.
Friday...after a cool start...warm air advection aloft by veering low level
flow will lead to building inversion from h875 to near h75 mb
through 00z Sat. This could limit mixing and keep highs more in
the lower to middle 60s. But with plenty of insolation...expect
deeper mixing thermals to help some areas make into the upper
60s/near 70...so will advertise middle to upper 60s widespread. Some
cirrus to try and spill in from the west off plains convection late in
the afternoon..otherwise a sunny day. ..12..
Long term...(friday night through thursday)
issued at 216 PM CDT Thursday may 23 2013
The extended remains potentially very wet...stormy...and a challenge
to accurately forecast temperatures. As might be the case anytime
this set of uncertain variables is used in one sentence during the
warm months of the year...this is all due to west to east stalled
boundary.
Models have trended somewhat closer to a blend between the
consistently southern European model (ecmwf)...and the consistently farther north
GFS. The balance of the two camps remains north with the
GFS/NAM/Gem...and south with the UKMET and European model (ecmwf). This is again
primarily due to how the models handle the high pressure over the
Ohio Valley in the wake of a strong East Coast system. For our
forecast...we remain under the threat of elevated storms...as
several rounds of low level jet induced mesoscale convective system affect locations north
of the surface front. This has been the case overnight and today
over Oklahoma...and was entirely missed by the 00z European model (ecmwf) which
appears too far south with the quantitative precipitation forecast and forcing today.
Thus...our forecast is a blend of the models...yet does not favor a
light rain scenario...vs a preferred elevated shower and thunderstorm
threat. That is not to say that a stratiform rain region or two will
affect the County Warning Area this weekend...with periods of time without thunder
taking place.
Models continue to show moisture convergence...with precipitable water values over
1 inch Saturday night through Tuesday...thus...repeat rounds of
rain/thunder are expected...with increasing amounts of widespread
heavy rainfall potential.
As we approach middle week...models suggest the boundary will lift
north...as the upper pattern amplifies. This could allow for heat to
build in with capping...which the 00z European model (ecmwf) did...but it is far from
certain as the 12z European model (ecmwf) keeps the front nearby with active...and
likely severe mesoscale convective system potential.
Thus...we generally will be quite cool over the weekend as rain
falls through the dry dewpoint air during the advection process...
then as the airmass transitions to warm sector...we should push
highs well into the 70s and 80s for middle week.
Ervin
&&
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 630 PM CDT Thursday may 23 2013
VFR conditions expected the next 24 hours. Northeast winds around
10 kts to fall off to light and variable overnight...then increase
out of the southeast but still at or less than 10 kts. Le
&&
Climate...
issued at 216 PM CDT Thursday may 23 2013
Record lows for may 24...
Moline.........36 in 1925
Cedar Rapids...34 in 1925
Dubuque........35 in 1925
Burlington.....38 in 1925
&&
Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&
$$
Synopsis...12
short term...12
long term...Ervin
aviation...le
