Area forecast discussion
National Weather Service quadrant cities Iowa Illinois
630 am CDT Sat may 18 2013
Synopsis...
issued at 245 am CDT Sat may 18 2013
06z surface analysis has a mesoscale wake low near kphp with a mesoscale high
north of konl. Numerous outflow boundaries were across the Dakotas
from the mesoscale convective system. The main frontal boundary ran from central Ohio...
across northern Illinois...and then into southwest Minnesota. Dew
points south of the frontal boundary were mainly in the 60s. North
of the frontal boundary dew points were in the 40s and 50s.
&&
Short term...(today and tonight)
issued at 245 am CDT Sat may 18 2013
Quiet and dry conditions will be seen across the area today as the
upper ridge moves east from the plains. Clouds from the northern
plains mesoscale convective system should initially provide filtered sunshine before
breaking up during the day.
Tonight...quiet and dry conditions will be seen during the evening
as the upper ridge moves into the western Great Lakes. After
midnight the mesoscale convective system and lift tools suggest elevated rain showers with possibly
some thunder should begin developing across the western County warning forecast area as the
low level jet begins to veer slightly into eastern Iowa with better warm air advection aloft
and moisture.
08
Long term...(sunday through friday)
issued at 245 am CDT Sat may 18 2013
Lower end severe weather risks late Sunday and again Monday the
main forecast issues with decent rains lasting into Wednesday.
Overview...initialization and verification adequate on synoptic
scales but poor on bl moisture and especially convective events.
This impacts forecast with conceptual forcing tools weighted
toward hi-res European model (ecmwf) best with GFS serious convective feedback and
NAM-WRF not much better. D_prog_dt supports use of more stable
hi-res European model (ecmwf) entire period with inputs from Gem-relative humidity and UKMET.
Sunday...trends of jet support lower end severe risk mainly in
the late PM into evening hours. Jet axis and forcing are delayed and
better focused well SW of area with little surface based forcing
noted at this time. Probable storms and showers to move into area
late PM and more likely in the evening. Sbcapes at or above 2000+ j/kg
suggested and wbz of ~11k above ground level with 35-45kt low level jet of a
convective system or line with some bowing segments. If surface
temperatures/dewpoints are at or above 78/65 then some winds of 60 to
possibly near 70 miles per hour may occur. Limited scl shear noted to
preclude tornadic threat at this time. Storms that can entrain middle/upper
dry level air may produce some large hail up to 1.5 inches but
this may not occur if mesoscale convective system is in mature stages as suggested. Highs
Sunday with partly sunny skies 83-88f northwest to southeast. Sunday night to be
mild with 64-68f readings for mins. Rain amounts most areas to be
light to moderate with isolated heavy amounts with any training of
storms which are marginal at this time with fast flow at this time. 'Pops high
chance to lower end likelies around 60 percent.
Monday...front nearby with fast upper flow supports PM scattered
redevelopment with potentially higher risk of severe weather in PM
hours than Sunday and any forcing. T/dew point profiles a few degrees
lower than Sunday but more favorable shear profiles for severe
with straight line winds of 60-70+ miles per hour due to good momentum
Transfer and even isolated tornado as jet axis impinges in with
decent scl shear. Hail over 1.75" possible if middle levels are as
dry as currently suggested. Probability of precipitation 40-50 during day and likelies
Monday night with another mesoscale convective system probably to move across area. Severe
risk should wane by middle to late evening hours. Maximum temperatures 78-83
with mins of 60-65. Rain amounts mostly light to moderate with
isolated heavy amounts and greater risk of training of storms with
parallel flow.
Tuesday into Wednesday...showers and isolated storms likely with
wave to rotate north from Southern Plains. This should be a
widespread rain event of moderate to heavy totals based on upper
forcing. Total rain amounts over the next 96 hours should be 1-3
inches over the forecast area. Highs in the 70s both days with
Wednesday a few degrees cooler than Wednesday as upper low moves
overhead. Mins middle 50s to lower 60s.
Thursday and Friday...large Canadian high pressure to bring cool
and dry air into region with highs upper 60s to lower 70s and lows
upper 40s to lower 50s with lows Friday am possibly still at least
a category lower suggested.
Nichols
&&
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 626 am CDT Sat may 18 2013
Frontal boundary running from near kind...to kmli...and kmiw has
resulted in MVFR/IFR conditions along and south of the front.
Conditions will improve to VFR by 18z/18 and remain VFR through
06z/19. After 06z/19 the potential for nocturnal rain showers/thunderstorms and rain will be
on the increase across eastern Iowa with the potential for MVFR
conditions prior to sunrise. ..08..
&&
Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&
$$
Synopsis...08
short term...08
long term...Nichols
aviation...08
