Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1159 am CDT Thursday Jul 24 2014

Short term...(today and tonight)
issued at 354 am CDT Thursday Jul 24 2014

Stout upper ridge remains centered over Colorado this morning...with
its associated ridge axis extending up through the central Dakotas.
This ridge has a very warm eml associated with it /see +17c 700 mb temperature
on the unr sounding last night/ as we continue to see shortwaves and
associated storms rotate around the periphery of the ridge...the
most impressive of which this morning is up in north central
Montana. By tonight the ridge axis will shift into Minnesota...though will
be getting flattened out by the 500 mb low currently over Washington
that will move into the Canadian prairies overnight.

This morning...high pressure centered over Western Lake Superior has a
cool a dry airmass in place that will likely delay the arrival of
precipitation. Have cut back considerably on probability of precipitation through the
afternoon...with most guidance showing the day going by dry as the
low level jet and Theta-E ridge look to remain across the Dakotas through the
day. The only thing to watch will be that Montana wave that will be
diving southeast across nodak this morning as it works around the ridge.
Nmm/arw wrfs show remnants of this activity working across western Minnesota
this afternoon...but considering the rap does not show the elevated
instability making much progress across the Dakotas today...favored
the dry forecast for today highlighted by the deterministic models.
Basically...left some slight chances through the afternoon SW of the
Minnesota river...closer to where the better moisture transport into southeast
sodak will be. Otherwise...few changes were needed for today...with
srly winds bringing in slightly warmer air resulting in highs a
couple of degrees warmer than what we saw Wednesday.

Tonight looks to bring our best chance for precipitation over the next
week. Some model disagreement still exists...with a couple of camps
existing with the NAM/GFS/ECMWF continuing to highlight the
potential for widespread elevated convection from south central Minnesota
into NE Iowa...while the Gem and WRF based cams show considerably less
activity in the mpx area...with two areas of convection developing
overnight down across Iowa and across central/northern Minnesota. The first of the
solutions maintains good continuity with the existing forecast...so
favored this forecast toward that Camp as this also matches up well
with expected evolution of the low level jet as it strengthens up into SW
Minnesota after 00z and veering into Iowa overnight...with storms developing
on the nose of the low level jet and edge of the capped eml. Though not
expecting widespread severe weather...given strength of elevated
instability moving in...along with effective bulk shear around 40
kts...could certainly see a few stronger cells capable of producing
large hail...but for the most part...activity should remain sub
severe.

Long term...(friday through wednesday)
issued at 354 am CDT Thursday Jul 24 2014

Scattered showers and thunderstorms should be in progress across
eastern Minnesota and western WI Friday morning in an axis of low level
moisture transport...an approaching middle level short wave and
coupled upper level jet. The NSSL...Storm Prediction Center and arw WRF/S depict the
situation well with the nmm WRF lagging a bit to the northwest. The
showers and thunderstorms will diminish across western WI in the
afternoon. Middle level temperatures will be rising into the 12-16
degree c range across central and southern Minnesota during the day on
Friday and this should aid in capping any further development
along a weakening cool front across western Minnesota. Dry weather is
then expected over much of the forecast area Friday night and Saturday.

A compact vertically stacked low pressure system remains on track
to drop southeast across the upper Mississippi Valley Saturday
night and Sunday. Layer moisture and forcing is best to the north
and east of the Twin Cities where high chance probability of precipitation for showers and
isolated thunderstorms continue. Low chance probability of precipitation are in place
from the Twin Cities on west and south. After highs on Saturday in
the lower to middle 80s...highs on Sunday will drop into the lower
to middle 70s.

The trend of cooler than normal temperatures will persist at least
into the middle of next week as a deep upper low/trough takes
shape over eastern North America while massive ridging builds in
the far west. Hence...a northwest upper flow will prevail across
the forecast area for much of next week. It looks pretty dry with no probability of precipitation
mentioned Sunday night through Tuesday night. Small chance probability of precipitation
begin to creep back in on Wednesday over the WI County Warning Area as well as the
southwest corner of Minnesota. Highs in the lower to middle 70s on Monday
will rise into the upper 70s to around 80 by Wednesday.

&&

Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1143 am CDT Thursday Jul 24 2014

Radar trends suggest scattered activity to move into western Minnesota
this afternoon. Believe it will hold off at kstc and east through
most of the evening with the best chance moving in after 06z
across the southeast portion of the area. Will bring in some
thunder to krwf this evening with perhaps a rain showers this afternoon
before 23z. Will spread this east overnight...leaving activity out
of west central Wisconsin doe to uncertainty. Cape builds into
Friday and may see some threat of widely scattered activity along
and east of the front into the afternoon. Appears frontal passage will only
make it into western Minnesota during the afternoon...and exiting wc
Wisconsin after 06z Sat. Some threat of MVFR ceilings
developing late tonight...especially if a more widespread mesoscale convective system
develops. Still some uncertainty to coverage...so will leave VFR
into Friday.

Kmsp...
will continue to mention prob30 thunderstorms and rain in the 08z-12z period...per
model discrepancy in overall development/placement during the
night. Trends should favor something developing farther east after
06z Friday...like we have it as low level jet and instability gradient shifts
east. Some threat of MVFR ceiling into Friday morning...but will leave
VFR for now due to low confidence. Still some threat of thunderstorms and rain into
Friday ahead of slow moving front into the afternoon...but
believe it will be rather isolated in nature and will leave this out
for now. Southeast to south winds ahead of front becoming west
into Friday evening.

/Outlook for kmsp/
Friday...chance MVFR ceilings/isolated thunderstorms and rain. Winds south-southeast at 5-10kts.
Sat...VFR. Winds west-southwest at 5-10kts.
Sun...VFR. Chance rain showers/MVFR ceilings. Winds northwest at 10-15 kts.

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$

Short term...mpg
long term...rah
aviation...dwe

National Weather Service Glossary of Abbreviations