Scientific Forecaster Discussion
Return to Local Conditions & Forecast
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
401 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 18z tafs through 18z Monday afternoon)
issued at 1242 PM CDT sun Apr 20 2014
Two concerns for this forecast cycle. The first is rain showers/thunderstorms and rain
chances along stalled frontal boundary from SW Minnesota through NE WI
while the second is dense fog late tonight and early Monday along
aforementioned boundary. Various 12z WRF solutions would point to
thunderstorm development by early this evening near the Iowa/Minnesota
border on eastward into WI. This would be well south of Keau with
only a few showers indicated between krwf-kmsp and Keau. Latest
WRF trends have also backed away from overnight activity arriving
from the west. With less clouds and showers there will likely be
more of a risk of dense fog late tonight and early Monday...
especially for Keau where a 1/4sm fog is now in place from 09z-13z.
Northwest winds will increase significantly Monday morning from kaxn to
krwf in the wake of a cold front. Speeds will approach 20 knots by
late morning with gusts near 30 knots. Increasing northwest winds for the
eastern taf sites by early in the afternoon.
Kmsp...it appears that any significant rain showers/thunderstorms and rain activity will be
well south and southeast of the airfield late this afternoon and early
this evening. MVFR visibility possible late in the night before winds
shift to the northwest shortly after 12z. Speeds increasing to near 20
knots for Monday afternoon with a few gusts reaching 30 knots.
/Outlook for kmsp/
Monday night...VFR. Northwest 10-15 kts.
Tuesday...VFR. Northwest wind less than 10kts becoming variable less than 5kts.
Wed-Thu...MVFR ceilings and visibilities with rain likely. IFR conditions
possible along with a chance of thunderstorms. Southeast wind 10-20 kts becoming SW.
Minnesota...Fire Weather Watch from Monday afternoon through Monday evening