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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1117 PM CDT sun Apr 20 2014

Updated for 06z aviation discussion...
issued at 1112 PM CDT sun Apr 20 2014

&&

Short term...(this evening through monday)
issued at 355 PM CDT sun Apr 20 2014

A nearly stationary front meanders from north of Eau Claire to
Fairmont. The boundary then becomes more diffuse heading southwest
into northeast Nebraska. Instability is increasing along and south
of I-90 although lapse rates are having a harder time after all the
convection this morning. Short term WRF solutions point to
convective development near the I-90 corridor by 23z. Visible
satellite imagery would surely support some towering cumulus west of
Spencer Iowa. Hence...much of the activity early tonight will be just
south of our forecast area.

Some additional showers are possible during the overnight hours
across central and southern Minnesota as a northern stream short
wave approaches. The middle level flow is actually diffluent heading
into west central Minnesota as some of the air is peeling off to a
southern stream short wave lifting northeast through the central and
Southern Plains. The models have struggled with this scenario for
the past several days with the NAM pretty steadfast on keeping it
dry. Even the European model (ecmwf) backed down today on the widespread quantitative precipitation forecast for
tonight. Therefore...allowed only a few light showers into west
central Minnesota during the overnight with areas around and north of the
Twin Cities remaining dry.

A cool front associated with the northern stream energy will sweep
across the forecast area early on Monday. Wind speeds will increase into the 20
to 25 miles per hour range across west central through south central Minnesota
by afternoon. The strong winds will combine with rapidly lowering
relative humidity values. Relative humidity values near 25 percent are likely
during the middle to late afternoon hours. This meets red flag warning
criteria and coordination with fsd and abr resulted in a Fire
Weather Watch for the afternoon and early evening across west
central...southwest and south central Minnesota. Used mix-down for
highs on Monday from the NAM at 800 mb. This yielded highs from
around 60 to near 70 from the Twin Cities on east and south.

Long term...(monday night through sunday)
issued at 355 PM CDT sun Apr 20 2014

Active pattern is expected through the long term with a few days
of wet weather and trend back to below normal temperatures late this week
with an established long wave trough.

High pressure settles in on Tuesday between the aforementioned
surface trough and cold front set to move tomorrow and another
eastward advancing trough set to arrive on Wednesday. We lowered
temperatures a bit on Tuesday and Wednesday based on recent
temperature verification and the cloud/precipitation trend on Wednesday.
It appears we will have our heaviest pure widespread rain event/S/
Wednesday night-Friday morning since last fall. On Wednesday...good warm
advection kicks in and we should get widespread isentropic lift
near the 1000-500mb thickness ridge. The instability is
meager...but the middle level lapse rates aren't terrible and that
combined with good 925-850mb moisture transport should support at
least isolated thunderstorms. The actually track of the surface
low has been tough to nail down given the lack of run-to-run
consistency and lack of overall model agreement. In general...the
GFS/NAM have tracked the system a little faster with time and
farther southeast. This has lowered our expectation for strong to
severe storms on Thursday...because now the instability doesn't
have time to build on Thursday before the low and boundary come
through. The GFS/European model (ecmwf) are also deeper with the low and linger the
system longer on Thursday. So...even though the severe weather
threat is diminished...the threat for a widespread 0.50"-1.5" of
rain remains. The European model (ecmwf) would even have accumulating snow on the
back side of the system Thursday night. The Gem linger the 500mb
low even longer and has 1-2.5" across most of the forecast area.
Strong cold advection will drop temperatures for Fri/Sat/sun...we'll have
to watch the temperature trend as we may be too warm with our forecast
during this time...and we could end up with 40s for highs a couple
of those days.

&&

Aviation...(for the 06z tafs through 06z Monday night)
issued at 1112 PM CDT sun Apr 20 2014

Confidence is fairly high in the timing of the cold front which
will cause the winds to shift out of the northwest. Confidence is
less in the development of precipitation overnight...along with fog.
Based of the hires models and current conditions feel that
krwf...Keau...and kmsp have the best chance for precipitation...while the
highest fog potential is Keau and krnh. On Monday northwest winds
will gust near 25kts.

Kmsp...
a few light showers are developing west of the airfield...so have
vcsh during most of the overnight hours...with a tempo shower
group centered around the highest probability for measurable
precipitation. Thunder is not out of the question...but the confidence is
too low to include in the tafs.

/Outlook for kmsp/
Tuesday...VFR. Winds northwest at 5-10kts.
Wednesday...MVFR with IFR/rain and thunderstorms and rain possible. Wind southeast at 15g20kts.
Thursday...MVFR with IFR/rain and thunderstorms and rain possible. Wind west-southwest at 20g30kts.

&&

Mpx watches/warnings/advisories...
Minnesota...Fire Weather Watch from Monday afternoon through Monday evening
for mnz047-054>056-064-065-073>075-082-083-091-092.

WI...none.
&&

$$

Short term...rah
long term...clf
aviation...jrb