Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
717 am CDT Sat may 18 2013
Short term...(this afternoon through sunday)
issued at 348 am CDT Sat may 18 2013
Today-tonight...broad-scale ridge axis just east of the area this
morning...and will continue to shift east while a large broad-scale
trough shifts east through the 4-corners region. Though overall
ridging has shifted east...minor bubble ridges within the developing
SW flow will prevent fairly widespread precipitation from
developing during the day today. However...that does not rule out
isolated to scattered convection from this morning through the day today.
Have already seen a handful of severe thunderstorm warnings...including some
verifying with hail as large as 1.5 inches. Storm intensity will
generally stay on the tame side of severe through much of the day today
while conditions ramp up for the potential for isolated severe thunderstorms
later this evening and tonight. One low pressure center identified over the
western Dakotas this morning will work in tandem with another low pressure
center over western NE/KS. As the northern low shifts NE...it will help
drag a warm front NE through southern and central Minnesota. This will not only allow
a surge of warm air into lower Minnesota...pushing high temperatures into the
low-middle 80s...but also maintain dewpoints into the 60s. Then...as
the upper ridge shifts further to the east...more pronounced
meridional flow with lowering heights will enhance lift. Steep
lapse rates along with a tongue of much higher instability will
surge into western Minnesota tonight...helping enhance the coverage and
intensity of thunderstorms tonight. Storm Prediction Center maintains a slight risk of severe thunderstorms
in its swody1...but the timing is still a little uncertain.
However...looking at the evolution of the trough and the
maintenance of ridging through the first half of the day...will
highlight this evening through tonight as the period where severe thunderstorms look
to occur. Main hazards would be large hail and damaging winds...with
isolated tornadoes as a secondary hazard since conds are less
favorable for tornadoes.
Long term...(sunday night through friday)
issued at 348 am CDT Sat may 18 2013
The more signficant threat for severe weather affects the region
Sunday and Sunday night. Southerly flow will be in place across
the area as the upper level trough digs into the southern and
Central Plains. The surface cyclone is forecast to deepen as it
moves toward northeast Nebraska by Sunday evening. Will likely see
activity wane from the Saturday night convection over the County Warning Area into
Sunday morning. With the unstable airmass in place..redevelopment
may occur quickly during the day. The focus should shift west
again in the afternoon along the main surface boundary nearer the
Nebraska low. A more significant wave lifts northeast Sunday night
as the upper low pivots slowly east. Forecast sounding for msp
indicates around 2000 j/kg cape with steep middle level lapse rates
7.5-8 c/km. 0-6 km shear values increase to 35 to 45 kts during
the evening as the wave rotates northeast. Hail and damaging winds
will be the main threats...but will have to monitor location of
surface front and occluding low later into the evening for any
possible tornado threat. Mesoscale convective system development will likely occur into
southern Minnesota...with heavy rain also possible as precipitable water is forecast to
exceed 1.6 inches.
The occluded system is forecast to sag slowly to the southeast
Monday into Tuesday. Will likely still maintain a thunder threat
through this period. Could see some strong storms yet in the
eastern County Warning Area (mainly wisconsin) for Monday afternoon. This will all
depend on how much daytime heating and destabilization can take
place. Again heavy rain will be possible...with widespread 1 to 2
inches forecasted from Sunday through Monday night.
Temperatures will cool back to below normal readings Tuesday
through Thursday...with extensive cloud cover remaining in the
area. Warmer and drier conditions should follow thereafter as the
upper low exits the area. Upper level heights/ridging aloft
develops and this should extend into at least the first half of
next weekend.
&&
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 650 am CDT Sat may 18 2013
Tricky taf set this morning due to the timing of precipitation into and
out of each terminal...including thunderstorm timing/duration...so plenty
of radar monitoring will be necessary. Surface warm front over southwestern Minnesota will
slowly lift north and east today...nudging the precipitation shield slowly NE with
it. Still dealing with plenty of convection this morning that has
been hitting the Minnesota terminals this morning...and will likely be
hitting the WI terminals later this morning into the early afternoon hours.
As thunderstorms impact the terminals...will see visibility drop into MVFR and
likely IFR ranges while ceilings hit the MVFR range /not expecting
IFR ceilings with tstms/. Morning bands of precipitation look to exit the
terminals between 16z-18z...then a prolonged break through the
rest of the daylight hours will be upon all sites. A cold front will
begin to approach from the west tonight. Ahead of this cold front...
additional showers/thunderstorms will shift into the region from the west. Have
timed it into the western taf sites late this evening...transitioning eastward
through the early morning hours on Sunday.
Kmsp...several rounds of rain/thunderstorms and rain this morning at initialization time
but difficult trying to pin down the ending time as several bands
have formed west of msp and are driving east. At this time...best timing puts
a break between 14z-16z...with the precipitation holding off until late
tonight. Could see a few showers move across late this morning into early
afternoon...but at that point the warm front should be north of msp...helping
emphasize a break in the precipitation. Tonight...as a cold front approaches...
additional rain/thunderstorms will develop over the area. Conditions will likely
drop to MVFR with ceiligns and possibly IFR with visibility. Will
monitor radar trends and issue amendments as necessary.
/Outlook for kmsp/
sun...VFR/MVFR ceilings. Chance rain showers/thunderstorms and rain with IFR. S-southeast winds 8-12 kts.
Monday...VFR/MVFR ceilings. Chance rain showers/thunderstorms and rain with IFR. S wind 10-15 kts.
Tuesday...VFR/MVFR ceilings. Chance rain showers/thunderstorms and rain with IFR. East-NE wind 5 kts.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...jpc
long term...dwe
aviation...jpc
