Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
324 PM CDT sun may 3 2015
Short term...(this evening through monday)
issued at 248 PM CDT sun may 3 2015
As of 2 PM...a cold front moved as far south as Redwood Falls to
Buffalo and Mora Minnesota. The front has slowed in the eastern
part of Minnesota and surge faster in SW Minnesota. This will likely set the
stage for convection further north than what models indicate.
Earlier convection across central Minnesota has led to more surface moisture
in central Minnesota compared to SC Minnesota where the cold front has not
reached yet. This reflected in the latest analysis of higher
MLCAPE where moisture has pooled along this front.
Regional radar along with satellite imagery indicated an area of
elevated rain showers near Huron South Dakota which will likely be the source of
convective initiation in SW/SC Minnesota around 4-5 PM as this wave moves
east-northeast across Minnesota. Short term models have been very inconsistent
with morning shra/tsra...but have been consistent with the
development of rain showers/thunderstorms and rain near the Twin Cities...NE to northwest
Wisconsin...with another area of rain showers/thunderstorms and rain developing along the
deeper moisture surging northward across Iowa later today. Probability of precipitation/weather
grids reflect this current trend with the highest probability of precipitation along the
Iowa/Minnesota border NE to Keau...but continued higher chance probability of precipitation as far
northwest as Redwood Falls to the Twin Cities and New Richmond
Wisconsin due to greater MLCAPES. Wind shear values are highest in
western/central Minnesota with the weakest along the Iowa/Minnesota border.
However shear values will likely increase along the Iowa/Minnesota border
during the evening. The best potential of severe thunderstorms and rain will occur after
3 PM...to 8 PM from Mankato northeast to Red Wing/southern suburbs
of the Twin Cities and from New Richmond to Eau Claire. This is
where both bulk shear values and MLCAPE are maximized. The main
threat will remain large hail and a few damaging wind gusts.
There is some indication of lingering rain showers/thunderstorms and rain across SC/southeast Minnesota
and into wc WI during the middle/late evening as a secondary wave
moves across Minnesota. There does remain enough instability to consider
chance probability of precipitation which has been included before midnight. Drier air will
filter into the region after midnight/Monday with temperatures near 70
for afternoon highs.
Long term...(monday night through sunday)
issued at 248 PM CDT sun may 3 2015
Cold front from Sunday evening will settle over Michigan/IL/IA/MO Monday night
into Tuesday morning...allowing for a brief touch of high pressure to scoot
across the area and suppress any potential precipitation to the S of
the mpx County warning forecast area early Monday night. However...as an area of low pressure
develops over the Colorado/Kansas region Monday night and picks up the remnants
of this fnt and upper level flow becomes more southwesterly to southerly...this
stalled fnt will start to trek northward as a warm front. A deepening trough
over the S-central Continental U.S. Will allow plenty of Gomex moisture into
the middle-upper miss River Valley regions Tuesday into Wednesday...and the more
widespread nature of the rain with the warm front plus the added
moisture looks to produce 0.50-1.00 inch quantitative precipitation forecast over much of the area
Tue-Wed. Embedded shtwv disturbances within the trough will aid in
convective development but will also produce pockets of enhanced
lift within an environment containing precipitable waters approaching 1.50
inches. The warm front may have trouble lifting entirely north of the mpx
County warning forecast area...potentially stalling near the I-94 corridor...Wed-Thu and
this would keep periods of rain with a few thunderstorms in the forecast for
Wed-Thu. It would also enhance low level moisture convergence and lift
in vicinity of the warm front so this may also enhance quantitative precipitation forecast amts. The cold front of
this system looks to push through the area Friday morning...allowing for a
reduction of probability of precipitation Friday into Sat...but the slow progression of the
fnt forces maintaining 20-30 probability of precipitation for mainly southern and eastern portions
of the County warning forecast area going into the start of the weekend. Then...for sun...
have maintained probability of precipitation there as the cold front looks to stall out just to
the east of the County warning forecast area while an area of low pressure develops along the
southwestern extent of the front and rides NE along it...producing
additional lift and dragging S-central moisture northward into the
system. Overall...a very wet pattern is certainly in store but
organized severe weather potential looks quite low.
As for temperatures...cooler values are expected Monday-Tuesday behind
the cold front of sun but when the fnt lifts back north...warmer air then
re-takes command and brings highs from the 60s Monday-Tuesday back to the
70s to near 80 Wed-Thu. The next frontal passage early Friday then allows highs
to drop back closer to normal values in the 60s and lower 70s
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1155 am CDT sun may 3 2015
Earlier convection across central Minnesota was not advertised well in
the short term models initially. However...the latest runs do have
some development along a cold front across central Minnesota through the
early afternoon hours. However...looking at development across SC/southeast South Dakota
which will likely be the trigger on more thunderstorms and rain by middle/late along
this front. There could even be a secondary wave of rain showers/thunderstorms and rain
behind the front in the early evening...but this scenario remains
low on the confidence scale. Best bet is continue the thunderstorms in the vicinity during
the afternoon...with a tempo which the latest guidance shows the
highest and most concentrated area of reflectivity on the radar.
Otherwise...most areas will see VFR after 3z...with some lingering
rain showers possible at Keau after 3z...through 6z. Winds will shift to the
north/northwest behind the front today...and become more north/NE Monday morning.
Kmsp...am following the latest short term models on the
expansion of higher radar returns around 20-22 northwest of the
terminal...and moving through the terminal area between 22-01z.
Timing will be adjusted if conditions warrant. Higher confidence
that the terminal will see a period of MVFR/IFR visibilities in thunderstorms and rain after
22z. Lower confidence on how long it will occur and ending time.
Winds will shift to the northwest/north after frontal passage with a more NE
flow Monday morning.
/Outlook for kmsp/
Tuesday...VFR early. Rain showers/thunderstorms and rain afternoon/evening with MVFR/IFR conds. Winds southeast
Wednesday...VFR. Chance MVFR/IFR conds in shra/tsra. Winds southeast 10-20 kts.
Thursday...MVFR conds likely with IFR conds possible in shra/tsra.
Winds S 10-20 kts.