Scientific Forecaster Discussion
fxus63 kmpx 180751
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
251 am CDT Wed Sep 18 2019
Short term...(today through thursday)
issued at 224 am CDT Wed Sep 18 2019
Surface analysis early this morning shows a nearly north-south
oriented cold front over the central Dakotas, emanating from a
surface low pressure center neat the Manitoba/Saskatchewan/North
Dakota triple point. A warm front from this low extends eastward
along the international border into the Great Lakes. Aloft, a deep
ridge resides to the east of Minnesota/WI, from the lower Mississippi
River valley into the eastern Great Lakes, while a compact upper
level low rotates over eastern Montana/Wyoming, which broke off
from a larger longwave trough sitting over the northwest Continental U.S..
Numerous showers/thunderstorms have broken out over western Minnesota
this morning within a highly moist (pwats between 1.70"-2.00") and
unstable airmass (mucape near 2000 j/kg) in the warm sector of the
aforementioned surface frontal system. The cold front is expected
to continue to slowly shift east which will push the rain shield
as a whole eastward. While most of the convection is expected to
remain elevated, a nearby low level jet and modestly steep mid-level lapse
rates could give way to some storms which may produce some small
hail and/or gusty winds. Already seeing wind gusts in the 20-30kt
range within the precip shield so there is some evidence that the
convection is bringing down the stronger winds aloft to the
surface. Severe storms cannot be completely ruled out given the
ingredients this morning but chances are still rather low of any
thunderstorms reaching severe limits.
Once this activity wanes this morning, the atmosphere will recover
this afternoon while still being in the warm sector with dewpoints
ranging from the mid 60s to lower 70s, especially in
southern/eastern portions of the weather forecast office mpx coverage area. Additional
thunderstorms are then expected to develop this afternoon through
tonight along and ahead of the front as the low level jet strengthens late
tonight. While the upper level support will shift off to the
northeast and become disjointed from the front, effectively
diminishing storm strength and as such limiting to nullifying
strong/severe storm potential, there will still be some pockets of
moderate-heavy rain in far southern Minnesota and western WI. The
precipitation coverage and intensity is expected to diminish
during the early morning hours Thursday through Thursday afternoon
but some scattered showers and thunderstorms will be lingering
through the day.
Another appreciable aspect of this frontal passage will be The
Drop in temperatures from the unseasonably warm values experienced
the past couple days. Highs today and Thursday will run in the
upper 70s to lower 80s. And, while lows early this morning will
run as high as the upper 60s to lower 70s, lower early Thursday
morning will drop to the mid 50s to lower 60s.
Long term...(thursday night through tuesday)
issued at 224 am CDT Wed Sep 18 2019
The long term period will begin warm and humid, with southwest
flow continuing through Saturday. An amplified upper trough will
work trough the area this weekend, cooling things off by Sunday.
Thunderstorms chances associated with this system look best Friday
night into Saturday. Another digging trough across the western
Continental U.S. Early next week looks more and more likely, which would
bring back deep southwesterly flow and increasing temperatures for
middle of next week.
By Thursday evening, the main feature of interest is the amplified
upper trough which will be centered over Idaho through Nevada at
that time. Through the following 24 hours, the trough will
progress east, but begin lifting northeast especially Friday
afternoon. Theta- E advection locally will increase late Thursday
into Friday as the frontal boundary that was just to our south on
Thursday lifts north through southern Minnesota and western WI by Friday
morning. Guidance continues to suggest convection will be possible
during the day Friday, but this is rather uncertain given lack of
large scale forcing. By Friday evening, pv advection with subtle
ripples in the upper flow ahead of the main trough will reach our
local area, and with about 2,000 j/kg MUCAPE and modest shear,
thunderstorms are expected to develop and advect in from the
eastern Dakotas. There is a risk of large hail and damaging winds
with these storms.
The cold front looks to reach western Minnesota midday Saturday, working
through the remainder of Minnesota and western WI by early Sunday
morning. Dew points will fall into the 50s and temperatures will
be very close to normal as we head into next week.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1105 PM CDT Tue Sep 17 2019
Did not change tafs much from what we had at 00z. Think activity
in sodak is probably what we will be dealing with the rest of the
night. The problem here is this is farther west and earlier than
anything was indicating tonight. Models that got closest to
getting this development correct was the hopwrfs, so followed
those for timing, which wasn't far off of what we had going. It's
looking increasingly likely we will see an MVFR cu field develop
Wednesday morning along the front, looks to bring a period of MVFR
cigs to stc with maybes at msp/mkt. Thunderstorms look to develop
along this front around 00z, with a threat for ts existing at eau.
Kmsp...shra/ts arrival could be as early as 9z or as late as 13z.
Also still a chance this dies before ever reaching msp. If we do
see showers, they look to last no longer than 2 hours from when
they start. Also a chance we could briefly see 2-3k ft cigs around
/Outlook for kmsp/
Thu...VFR. Chc MVFR/thunderstorms and rain late. Wind southeast 5 kts.
Fri...VFR. Chc MVFR/tsra. Wind S 10g20 kts.
Sat...VFR. MVFR/thunderstorms and rain likely in mrng. Wind SW bcmg west 15g25 kts.