Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Twin Cities/Chanhassen Minnesota
710 am CDT Wednesday Apr 1 2015

Short term...(today and tonight)
issued at 422 am CDT Wednesday Apr 1 2015

Warmest temperatures of the year...followed by afternoon
thunderstorms and the potential for the first severe weather this
season continues to be on track for today.

Increased afternoon highs for today...and would not be surprised to
80f across southern Minnesota given the warm air advection...deep
mixing...and diurnal heating. Forecast soundings show 40kt gust
potential with the south southwesterly winds ahead of the cold
front...so continued with a Wind Advisory across the southern half
of the forecast area.

As alluded to in previous discussions...the source of the boundary
layer moisture is moisture advection in the h900-800mb layer. This
will take place along the NE/Iowa border...up through Redwood Falls.
Boundary layer mixing will bring this moisture down to the surface
causing dewpoints to rise. However...farther east in central/eastern
Minnesota...boundary layer mixing will fail to increase surface moisture
until late afternoon...so a red flag warning has been issued for
this area given the dry fuels...low relative humidity...and strong winds.

Convection certainly looks likely this afternoon...after 4pm...as
the hires models depict a line of storms from eastern NE up through
northwest WI. Given the instability and shear...severe weather is a
real possibility...and the slight risk has been shifted slightly
northward for this afternoon. The main threat is hail/wind
initially...followed by mainly wind 1-2hrs after initiation. The GFS
continues to be the fastest model in comparison to the other
deterministic models with the timing of the cold front. For probability of precipitation
trended toward a slightly slower/westward solution...but advanced
the precipitation faster in anticipation that cold pool development should
propagate the line faster then the cold front...so have precipitation
exiting the region by 09z tonight.

Long term...(thursday through tuesday)
issued at 422 am CDT Wednesday Apr 1 2015

Strong cold air advection and very deep mixing will make for another windy day
Thursday. Soundings show mixing up to 700 mb with unidirectional
flow. GFS is most bullish with the wind reaching solidly advisory
criteria...the others are a tad more reserved. Nonetheless...could
see gusts exceed 40 knots and may need a Wind Advisory for parts of
the area...particularly central Minnesota and northwest WI. Relative humidity will
plummet into the teens by afternoon and will set up another
critical fire weather day. Consult the fire weather section below for
more information on that threat.

Wind will ease quickly Thursday evening and high pressure will
build in Friday/. A fast moving weak clipper will slide southeast
across the northern plains and upper MS valley Friday night and
could bring a bit of light snow to northern MN/WI. Most of it will
remain north of the County Warning Area...but did introduce a slight chance
bordering weather forecast office dlh.

Models diverge from Sunday Onward with the European model (ecmwf) on the slower
side and the GFS on the faster side of the guidance consensus. GFS
has also shifted north with the system for next week whereas the
European model (ecmwf) has shifted south. There is too much uncertainty to get into
any specifics yet...but chances for precipitation increase during this
period and it looks like mainly rain.

&&

Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 710 am CDT Wednesday Apr 1 2015

Models have been trending slower and slightly further west with
thunderstorm initiation late today. Current thinking is they will
form from rwf to near stc around 23z...then slide east during the
evening reaching msp by 02z...rnh by 03z...and eau around 05z.
Shifted the timing back only slightly in the tafs and will await
further trends before making more changes. Strong southerly winds
will develop this morning with gusts exceeding 40 knots across southern Minnesota
which will persist until the storms push in. Winds should peak by
middle afternoon.

Kmsp...it is looking like storms will impact msp a bit later than
anticipated earlier. Left a large window for thunderstorms in the vicinity and a tempo
which will become better defined in further updates. Increased
wind speeds a bit for this afternoon with forecast soundings
showing potential for gusts to exceed 40 knots.

/Outlook for kmsp/
Thursday...VFR. Winds northwest 10 kts in the morning becoming west 20g35 kts in the
afternoon.
Friday...VFR. Winds northwest 10-15 kts.
Sat...VFR. Winds west 10-15 kts.

&&

Fire weather...
issued at 422 am CDT Wednesday Apr 1 2015

Strong southerly winds from 25 to 35 miles per hour will develop this
morning across the red flag warning area and persist through the
afternoon while humidity levels drop to around 25 percent. If
winds are stronger than currently forecast further north...a few
counties may need to be added to the warning.

A Fire Weather Watch has been issued for Thursday from southwest
to northeast Minnesota. Strong west winds from 25 to 35 miles per hour will
develop during the morning and persist through late afternoon. In
addition...humidities will drop into the 15 to 20 percent range
setting up another day with critical fire weather conditions. The
watch is in effect west of the area expected to get hit most by
thunderstorms this evening...as there is potential for wetter
fuels there.

&&

Mpx watches/warnings/advisories...
Minnesota...red flag warning from noon today to 7 PM CDT this evening for
mnz076>078-083>085-091>093.

Wind Advisory until 5 PM CDT this afternoon for mnz064-065-067-
073>076-082>085-091>093.

Fire Weather Watch from Thursday morning through Thursday
evening for mnz042>045-048>062-064>068-073>075-082.

WI...none.
&&

$$

Short term...jrb
long term...borghoff
aviation...borghoff
fire weather...borghoff

National Weather Service Glossary of Abbreviations