Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
650 PM CDT Monday Jul 28 2014
Short term...(this evening through tuesday)
issued at 337 PM CDT Monday Jul 28 2014
Short term concerns remain timing of showers this evening and the
threat of showers/thunder for mainly Tuesday afternoon.
The initial short wave across southwest Minnesota is shearing/weakening
to the southeast. Heavy cumulus noted...and perhaps a light
shower affecting south central Minnesota per latest radar trend.
Overall...this should exit through 00z Tuesday. Water vapor imagery
shows another short wave dropping southeast over the western Great
Lakes with some rain showers associated. Several deterministic models show
some weak convection affecting west central Wisconsin overnight.
Several hires models indicated this as well. Instability is weak
but there may be enough forcing with the wave to generate a few
showers/isolated thunder. Clouds will thin some...but do expect at
least some scattered clouds to remain overnight.
On Tuesday...models continue to suggest another more potent short
wave affecting at least west central Wisconsin mainly during the
afternoon. MUCAPES increase to around 1500 j/kg over eastern Minnesota
and western WI with deep layer shear around 30kts. Middle level
lapse rates not that unstable...so severe threat not that high.
Perhaps some marginal severe hail. Should see high temperatures
warm through the 70s to some lower 80s across the area.
Long term...(tuesday night through monday)
issued at 337 PM CDT Monday Jul 28 2014
The prevailing upper level pattern through Saturday will be a
large ridge over the western Continental U.S....a deep longwave trough over the
eastern Continental U.S....with the central Continental U.S. Caught in the middle underneath
fairly persistent northwest flow. At the surface...this will result in mainly
surface high pressure. Although occasional shortwave disturbances will
swing around the western fringes of the longwave trough...through the
upper miss River Valley and Great Lakes...the lack of moisture
combined with weak surface support due to high pressure keeping any
organized frontal systems away will mean only isolated precipitation
development for mainly far eastern Minnesota into western WI.
Going into the weekend...this longwave pattern begins to break
down as the western ridge shifts into the central Continental U.S.. this will
also mean a breakdown of the persistent high pressure...allowing weak
surface low pressure areas to infiltrate the central Continental U.S.. this means a
slight increases in probability of precipitation for the entire County warning forecast area /as opposed to mainly eastern
portions of the weather forecast office mpx County warning forecast area/ for the weekend into early next
week. Still not looking at much in the way of quantitative precipitation forecast...so probability of precipitation are
kept in the 20-30 range. In fact...overall quantitative precipitation forecast over the next week
will struggle to reach a quarter inch and many portions of the
County warning forecast area will remain dry.
As for temperatures...the pattern still allows for very little day
to day variation in temperatures due to the lack of airmass
change. Highs through the weekend will hit the upper 70s to lower 80s
while lows drop to the upper 50s to lower 60s.
Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 650 PM CDT Monday Jul 28 2014
VFR conditions expected through the period. There will continue to be
stratocu around 5000-6000 dropping southward from the Western
Lake Superior area. Some of this may go broken in parts of western
wisc later this evening or overnight. Otherwise little weather
tonight. Left fog out for the Keau area...due to likelihood for
the clouds to inhibit widespread fog formation.
Some showers are possible in western wisc Tuesday afternoon and
maybe thunder as well. Threat is not yet strong enough to include
thunderstorms and rain in the Keau taf. Northwest wind might gust above 10 knots amid
Kmsp... VFR through the period. There is a very small chance of
broken clouds around 5k-6k feet later tonight as clouds drop
southward but most of the broken clouds will be in Wisconsin. More
cumulus will develop late Tuesday morning and this is also when there
may be a few gusts 10-15 kts.
/Outlook for kmsp/
Wednesday...VFR. Winds northwest 5-10 kts.
Thursday...VFR. Winds northwest 5 kts.
Friday...VFR. Winds northwest 5 kts.