Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
627 am CDT Thursday Jun 20 2013
Short term...(today and tonight)
issued at 345 am CDT Thursday Jun 20 2013
Scattered high based showers and thunderstorms continue to plow
north-northeast over central Minnesota at this hour. Activity supported by warm
frontal boundary emanating from distant surface cyclone parked
over NE Montana and southern Saskatchewan. Several Special Weather Statement products
have been issued during the overnight for pulse T-storms
associated with this activity. Although no reports accumulated...
a few of these could easily have produced dime to maybe even
nickel sized hail. Hopwrf definitely handling this activity
better than any other short term prognosticator...so will continue
to call upon its services for short term painting of forecast into
this afternoon. Convergence at 250mb will sweep into SW County Warning Area early this
morning and overspread much of southern Minnesota by 18z. Most of present
shower activity will exit northern Minnesota County Warning Area by about 14z time frame.
Slight to chance probability of precipitation will remain in force over much of forecast area into this
afternoon...as abundant heating further destabilizes atmosphere with
lapse rates in the 6 to 7c range across the area. Looks like best
chance for severe weather erupts over most of the County Warning Area between
21/03z-21/09z...as strong Theta-E advection tags up with intense
divergence aloft per gfs40 250mb level...and 25 to 30kt 850mb low
level jet. Best cape values in the 2000-2800 joule variance...will
be encountered over SW Minnesota...with 1500 to near 2000 noted over
remainder of southern Minnesota. Looks like main threat for severe
weather remains wind and hail. Heavy rain also still a
possibility...as moisture transport vectors very strong over much
of the forecast area overnight. Increased temperatures this afternoon due to rising
850mb temperatures increasing southerly flow and plenty of diffuse
sunshine even with possible cirrus shield.
Long term...(friday through wednesday)
issued at 345 am CDT Thursday Jun 20 2013
Friday morning looks to start out with an ongoing mesoscale convective system in an exiting
and/or decaying Mode shifting through eastern Minnesota into western/northern WI. This
is in response to the broad-scale upper ridge having shifted into the
Great Lakes with a surface low pressure center ejecting eastward over northern Minnesota.
While having the mesoscale convective system would seemingly work over the area...
instability will be reinvigorated as a quasi-stationary ridge over the
plains brings deep Gulf moisture into the region and a broad-scale
trough over the western states shoves several shortwave disturbances
into the north-central Continental U.S.. as the atmos gains energy with the
heightened instability...persistent strong middle- and upper-level
jetting along with steep lapse rates will promote the development
of strong/severe thunderstorms by late Friday afternoon into the evening...possibly
again in the form of at least one east-west mesoscale convective system along a residual
warm front. This activity will quickly shift off to the east by Sat
morning...but its ingredients will remain in place which will set the
stage for another round of similar storms late Sat afternoon into Sat
evening. Continued low level warm/moist air...with dewpoints near 70
through the weekend...along with an approaching cold front and enhanced low-
level jetting within pronounced southwesterly flow...again look to promote
the formation of clusters of late day thunderstorms and/or at least mesoscale convective system
Sat evening/night. Hazards remain the same for both Friday night and
Sat night events - mainly large hail and damaging wind but the
enhanced jetting and veering with height makes isolated tornadoes
another highlight. There is more uncertainty with Sat evening events
since they will be highly dependent on what happens Friday night...
but there is still enough chance for Storm Prediction Center to put the entire area in
slight risk for day 2 /Fri/ with all of Minnesota and most of the weather forecast office mpx
WI counties in slight risk for day 3 /Sat/.
The cold front slowly progresses east over the region on sun...working
within a continued deep moisture profile. Daily precipitable water values Friday
through sun are at least 1.75 inches. Broad-scale lift with the fnt
and the lifting out of the northwest upper trough will transition the
hazard from severe weather to one of heavy rain/flooding. Precipitation totals
through the weekend may easily eclipse 3 inches...with some areas
possibly as high as 5 inches...including rates in the 1-2 in/hour
range. Precipitation chances wind down late sun into Monday as more zonal flow
gives way to a slight ridge within the flow for Tuesday. This feature
is also short-lived as another longwave trough moves in from the
west...keeping the wet pattern in place with scattered shwrs/tstms.
In addition...the primarily zonal flow will not allow for much
alteration in temperatures all through early next week. Highs will
continue in the 80s with lows around 70.
&&
Aviation...(for the 12z tafs through 12z Friday morning)
issued at 615 CDT Thursday Jun 20 2013
Convective shield noted over kaxn at this writing. Isolated
convection also noted over southeast Minnesota...and near Keau. All activity
trekking northeast at 20 miles per hour. Vcsh should vacate kaxn region
by 15z...and Keau by 16z. Increasing southeast flow anticipated by
late morning and continuing ahead of surface trough over
far eastern Dakotas. This feature will move little during
the next 48 hours. Ku rule indicating short term development
of 050-060 ceilings developing early in taf period as cirrus
shield over central and portion of SW Minnesota marches north or
becomes diffuse over much of southern Minnesota. Showers and T-storms
become much more numerous between 03z-09z across taf region
..as Theta-E advection...Isentropic analy and upper level
support maxes out for this forecast period. Could easily
encounter MVFR ceilings/visibilities with thunderstorms...and even short term
IFR ceilings. Lowest ceilings will be encountered after end of precipitation
at krwf and kaxn.
Kmsp...
Ku rule indicating short term strato-cumulus deck this afternoon.
Otherwise...look for increasing southeast flow ahead of surface
trough mentioned above. Shower and thunderstorms complex
should overspread kmsp by 03z...and last for several
hours. T-storm activity could easily plunge ceilings and visibilities
to MVFR status...with VFR conditions returning late in period.
/Outlook for kmsp/
Friday...VFR. Chance of MVFR/tsra. Southeast winds 5-10 kts.
Sat...VFR. Chance of MVFR/tsra. Southeast winds 5-10 kts.
Sun...VFR. Chance of MVFR/tsra. S winds 10 kts.
Monday...VFR. Chance of MVFR/tsra. S winds 10-15kts.
&&
Hydrology...
issued at 345 am CDT Thursday Jun 20 2013
A wet pattern is expected across the upper Mississippi River
valley region through early next week with flooding potential
virtually each day during this period. A very slow moving upper
air pattern will allow for several rounds of showers and
thunderstorms into early next week. Moisture levels will be on
the rise through Friday and the warm/humid air mass will remain
entrenched across the region into Monday. Daily precipitable water values are
prognosticated to reach over 1.75 inches through the weekend...which is
more than 2 Standard deviations above normal. Ffg values are quite
low with 1 hour values around 1.5 inches across the Minnesota River
Valley and south central Minnesota...with three hour values in these same
areas just under 2 inches. Areas that experience
thunderstorms...especially over the weekend...will likely have
rainfall rates approaching 2 inches per hour. Therefore...it will
not take much for localized flooding to occur.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...ajz
long term...jpc
aviation...ajz
hydrology...jpc
