Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
558 am CDT Friday may 22 2015
Short term...(today and tonight)
issued at 403 am CDT Friday may 22 2015
A quiet short term forecast with expansive high pressure dominating
the weather conditions through tonight. Clear skies and light winds
are expected today. The surface anti cyclonic circulation will
works its way further east during the day...and winds will
eventually become more southerly...but remain light. High
temperatures still look on track to being a couple degrees warmer
than yesterday...and model soundings indicate dry adiabatic lapse
rates from about 800mb down to the surface...which would yield temperatures
in the low to middle 70s. Dew point depressions will be quite large
again...with dew points in to the low to middle 30s by the afternoon.
Concern about precipitation late tonight has faded as model
consensus has trended toward the European model (ecmwf) solution of holding off any
precipitation development this far north from a developing system
off the Lee of The Rockies. However...cloud cover will be on the
increase as southerly winds aloft persist tonight. So...low temperatures
tonight should be a couple degrees warmer than last night.
Long term...(saturday through thursday)
issued at 403 am CDT Friday may 22 2015
Quite the unsettled pattern will commence for the region starting
Saturday and last through much of next week...mainly due in the
synoptic scale to a large dome of high pressure setting up over
the southeastern Continental U.S.. this will promote stoic southwesterly flow across the area
which will bring western Gomex moisture into the north-central Continental U.S. While
several surface and upper level disturbances ride northeastward along the western
periphery of the southeastern high pressure dome. An surface low pressure center will
develop over eastern Colorado/western Kansas Sat night into sun...then gradually
shift northeastward sun-Tue. Have slowed its progression as that has been
the trend in the NAM/ec combination...so have scaled back probability of precipitation on
Sat into Sat night. Best prospects for precipitation now look to be sun
into Monday...so that is when likely probability of precipitation are most prevalent. The surface
low pressure system is aided by a kicker upper level trough coming out of
the intermountain region Sun night through Monday night. With precipitable waters
rising to around 1.50 inches...and in some spots more...along with
weak lapse rates and meager shear/instability...not looking for
much in terms of severe weather but there may be some heavy rain
producers. This low pressure system lifts into the Great Lakes by Tuesday
morning...leaving a rather diffuse surface pressure pattern for Wed-Thu. With
the occasional upper level wave passing by within a continued moist
environment...it will not take much to produce isolated/scattered
showers and thunderstorms. Not looking for washouts for any of the days in
the extended as the precipitation will generally be of the hit-and-miss
variety but highest probability of precipitation do come over the Holiday weekend.
Temperatures will have little day-to-day variation over the
weekend through the first half of next week. Highs will continue
to run in the middle 60s to middle 70s with lows mainly in the 50s.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 554 am CDT Friday may 22 2015
High pressure in control means clear skies and relatively light
winds through the period. A system advancing from the southwest
toward the upper Midwest will begin to spread cloud cover in
tomorrow morning...but the low level cloud cover looks delayed and
wont arrive until later in the day tomorrow.
Kmsp...VFR. No change from main discussion.
/Outlook for kmsp/
Sat...VFR. Slight chance -shra/-tsra late. Winds S 5 to 10 kts.
Sun...VFR. Chance rain showers/thunderstorms and rain with MVFR or lower conditions.
Winds southeast 10 kts.
Monday...VFR. Chance rain showers/thunderstorms and rain with MVFR or lower conditions.
Winds S 10 kts.