Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1047 PM CDT sun Mar 29 2015
Short term...(this evening through monday)
issued at 355 PM CDT sun Mar 29 2015
Potent cold front continues to make gradual progress from Minnesota into
WI this afternoon. Strong winds have developed in the wake of the
front...some to the tune of 40-50 miles per hour /including msp Airport/...
along with clearing skies within strong subsidence mixing down low level jet
aloft. Any lingering precipitation has shifted east of the County warning forecast area into eastern WI
and remaining cloud cover will be soon to follow as the front
scours out the lower levels. Winds will gradually diminish
overnight as high pressure settles over the area...and will keep the
clear skies in place through tmrw morning. The high pressure respite will be
brief as a weak low pressure system will approach within northwest flow
aloft. Very little upper level support and moisture comes with
this system...and even that will be more focused into northern Minnesota than
in the mpx County warning forecast area...so the only probability of precipitation that remain will be slight chance
probability of precipitation for the northern and eastern fringes of the County warning forecast area...for light rain.
Otherwise...despite the northwest flow aloft...temperatures will continue on a
moderating trend tonight into Monday due a warm Air Ridge over the southwestern
states beginning to shift into the central Continental U.S.. though the clear
skies and lighter winds tonight will allow lows to drop to the low-
middle 30s overnight...highs tmrw will surge into the 60s in the Minnesota
portion of the County warning forecast area and into the 50s for the WI portion of the
County warning forecast area.
Long term...(monday night through sunday)
issued at 355 PM CDT sun Mar 29 2015
Only concern in the extended period is the potential of thunderstorms and rain
Wednesday afternoon/evening as a sharp cold front moves across the
Ec/GFS/Gem all have trended slower with the shortwave moving across
the northern rockies and into the northern plains Wednesday
night. The ec has been the most consistent and had the best
forecast for todays system with the slower movement and more
moisture a few days ago. The slower solution will have a major
impact on the development of rain showers/thunderstorms and rain Wednesday aftn/evening.
Previous runs had the main area developing southeast of mpx which seem
likely due to the initial strong cap and lower dew points.
However...with this slower movement 850 mb winds have increased
significantly ahead of this cold front.
Due to the slower solution and moisture advection expected ahead
of the front Wednesday afternoon...dew points will likely rise as
well. The current run of the ec have dew points nearly 55 degrees in
far SW Minnesota Wednesday afternoon. The GFS is even higher with 55-60 degree dew
points as far north as kmkt. If these higher moisture values in the
boundary layer surge northward across the upper Midwest as
forecast...the cap will weaken considerably during the afternoon as
temperatures rise into the 70s.
Although shear values are ample enough for organized convection...
MLCAPE will be dependent on the amount of boundary layer
moisture advecting northward ahead of the cold front. Current
forecast soundings of surface cape have nearly 1000-1500 j/kg on the
latest GFS run...with the ec a close second with nearly 1000 j/kg
during the middle/late afternoon hours. Severe weather is possible...especially
considering middle level lapse rates of /8.0 c/km from 70-50h/...wind
shear values and lower freezing level. Again...this is highly
dependent on the amount of instability.
Past Wednesday night...cooler weather will develop as the mean flow
becomes more west-northwest and thickness values decrease by the end of the
week. However...it should be short lived with a more west/SW flow
developing next week. In addition...normal highs for early April
are in the 50s. So even blw normal temperatures still mean highs above
Aviation...(for the 06z tafs through 06z Monday night)
issued at 1047 PM CDT sun Mar 29 2015
Light westerly winds overnight will back to the southeast early on
Monday as a wave of low pressure drops southeast across mm and WI
during the afternoon and evening. Added vcsh to krnh and Keau for
about a three hour period during the late morning/early afternoon
hours when a band of light rain may pass these sites. Still looks
VFR through the period at all sites. Winds will become west-northwest during
the afternoon across western Minnesota with speeds increasing to 10-15
knots with gusts from 20-25 knots.
Kmsp...an area of broken-ovc060-080 will pass across the airfield
overnight and Monday with scattered conditions developing by Monday
evening. Light west winds backing to the southeast Monday morning
and then returning more westerly by evening.
/Outlook for kmsp/
Tuesday...VFR. Winds northwest 5-10 kts.
Wednesday...VFR. MVFR/-shra possible in the aftn/eve. Winds S 20g35 kts.
Thursday...VFR. Winds west-northwest 25g40 kts.