Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1054 PM CDT Monday may 4 2015
Short term...(this evening through tuesday)
issued at 350 PM CDT Monday may 4 2015
High pressure atop the area today has suppressed cloud cover...allowing
for plenty of sunshine behind the cold front from yesterday which has stalled
out over the middle-miss River Valley and Central Plains regions.
Despite plenty of sunshine...cold air advection as evidenced by northerly winds all day
long has kept highs in the middle 60s to lower 70s. Clouds will increases
tonight as the high pressure center shifts off to the east and the stalled
front gains impetus to lift north as a warm front tonight through Tuesday. However...
per overall model trend from last night through today...this northward
progression will be slower and this will influence the timing of
the return of showers/thunderstorms into southern Minnesota Tuesday. In addition...a northwest-southeast
oriented upper level ridge axis will shift north-northeast across the area during the
day Tuesday...and this ridge will also keep the warm front along with any
associated precipitation off to the S. Therefore...have been able
to keep the forecast dry until the pre-dawn hours early Tuesday morning then
kept the precipitation only in far southern and southwestern portions of Minnesota Tuesday. Have
also kept probability of precipitation no higher than low-chance range due to the slower
progression...and also confined thunderstorm mention to Tuesday with no thunderstorm
mention for tonight. Temperatures look to run fairly similar tmrw as what
was recorded today...with highs in the upper 60s to around 70...due to
no appreciable temperature advection. Lows tonight will range from around 40
in northern portions of the weather forecast office mpx County warning forecast area to around 50 near the Iowa border.
Long term...(tuesday night through monday)
issued at 350 PM CDT Monday may 4 2015
The extended period can be characterized as unsettled/more humid
and an anomalous feed of deep moisture from the Gulf through the
weekend. Two fronts are forecast to move across the upper Midwest
which will focus a much better chance of organized convection...
heavy rainfall and associated higher confidence of likely or
categorical probability of precipitation. However...as moisture begins to surge northward
Tuesday...any period in the extended has a chance of rainfall.
Basically we need to focus on frontal passages which will increase
the likelihood of rainfall.
As for frontal passages...the first will occur Thursday...with a
second front late in the weekend. Both of these fronts and
associated moisture/energy parameters have the potential of severe
thunderstorms. However...the overall deep wind shear parameters
are not strong enough to warrant anything other than slight
The upper air pattern remains favorable for copious amounts of
deep Gulf moisture to progress northward across the plains and
into the upper Midwest. Precipitable waters anomalies are nearly 2-3 Standard
deviations above normal for this time of year by Thursday with
values near 1.30" to 1.50". The moisture advection parameters blw
70h are over the top with Standard deviations as high as 4-5 above
normal in the upper Midwest by Thursday...leading to a higher
probability of heavier rainfall totals once convection develops.
The main dilemma is where does the precipitation begin or focus as
the week progresses. There is a hint of a strong low level jet for Tuesday
night into Wednesday morning...but this focus is mainly in western
and northern Minnesota. Not until Thursday as the front moves through
Minnesota/WI does any type of a higher probability of heavy
rainfall/thunderstorms and severe weather develops.
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1054 PM CDT Monday may 4 2015
VFR through the period. Rain showers/thunderstorms and rain to remain south of the taf
sites through Tuesday morning as a dry east-northeast low level flow
prevails. The low level flow will veer to a more southeast direction
Tuesday afternoon...allowing for ceilings of 040-050 to spread
slowly north across the taf sites. Small chances for rain showers at krwf
Tuesday afternoon/evening with dry weather continuing elsewhere. Southeast
winds will be on the increase by late Tuesday morning with 12-16
knots sustained with gusts around 20 knots in the afternoon.
Kmsp...few concerns this cycle. East-southeast winds increasing Tuesday
morning to 12-14 knots with gusts 20 knots through the afternoon.
Ceilings of 040-050 developing Tuesday evening.
/Outlook for kmsp/
Wednesday...VFR. Chance MVFR 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.
Friday...VFR. Winds northwest 5-10 kts.