Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
430 am CDT Tuesday may 21 2013
Short term...(today and tonight)
issued at 328 am CDT Tuesday may 21 2013
The center of the surface low responsible for all of the sensible
weather the past few days continues to sit and spin /nearly
stationary/ across eastern South Dakota. Although there has been no
significant movement with the upper trough over the last 12
hours...the small 500 M height falls yesterday actually helped
deepen the surface low by 2-3 mb and perhaps even tighten up the
circulation and corresponding frontal boundaries across the area.
The attendant cold front stretching south across the central and
Southern Plains was responsible for focusing the violent weather
in the states to our south. But even this morning the stationary
boundary stretched out from west to east from the surface low
across central Minnesota and northern WI is the focus for widespread
showers and weak thunderstorms in these same areas. There is nice
middle level drying stretching from the Minnesota/WI border all the way
south into Kansas and OK. This drying will likely keep much of
southern Minnesota and portions of west central WI dry at least during
the morning. Closer to the middle level circulation in central Minnesota
/especially west central/ there should be light stratiform type
precipitation late this morning and afternoon where frontogenetical
forcing will be stronger. However...probably not a wise move to
completely remove probability of precipitation in the warm quadrant of the system across
southern Minnesota...because there should be enough afternoon instability
given decent bl moisture to pop some cumulus and afternoon showers.
There is still a decent thunder chance with any of the showers in
eastern and west central WI today. Available short-range WRF
guidance including The Hop-WRF /at hopwrf.Info/ support this.
Overall...the low fills and drifts southeast with time tonight.
There is still enough lift to warrant pop mention even with the
weakening trend...but do not expect heavy precipitation. Just pull up a
radar mosaic and look at the radars to our north
/kabr/kfgf/kdlh...those showers will continue to rotate
cyclonically around the low and when the low moves off to the
southeast...those showers will come along with it.
Long term...(wednesday through monday)
issued at 328 am CDT Tuesday may 21 2013
Cloudy...cool...and scattered to numerous light rain showers or
sprinkles are on tap Wednesday with the low still taking its time
to move across the forecast area. Really think by Tuesday night
the instability will be shoved far enough to the west that we
should just be dealing with the light showers and no thunder. We
are dry by early Thursday morning...but clouds should be slower to
clear. No major forecast changes in the Thursday-Friday time
frame. Went just a bit cooler with temperatures during this time.
The guidance trended that way...but simply think it is more to do
with slight changes in the timing of showers during the day on
Wednesday and clearing of clouds late Thursday night. This should
set the stage for a very cool Friday morning. Upper 30s are
certainly within reason across central Minnesota and west central WI with
the clouds moving out and that high moving in.
Medium to long range guidance continues to forecast troughs along
both west/east coasts and a ridge over the central states and a
closed anticyclone through the weekend into early next
week. Southerly flow ahead of the trough and surface low/warm front
development should focus precipitation over the Central Plains late in
the weekend and into the northern plains/mid-upper MS valley/Great
Lakes early next week where convection is likely as indicated in
the gefs/European model (ecmwf) ensemble members and GFS runs. There are a lot of
probability of precipitation in the extended...but it is difficult to remove them...even
given we have fairly low confidence in the timing and placement
of the showers and thunderstorms late this weekend and early next
week. Here's why its difficult to remove probability of precipitation. Climatology is
right around 25% for a 24 pop forecast this time of year. The
21.00z GFS has a longwave trough approaching from the west and
southwest flow here and the 21.00z European model (ecmwf) is less amplified and
even quasi zonal. Both of these patterns would be fairly active
and would certainly warrant keeping probability of precipitation at least at the
muted/averaged values of climatology.
&&
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1057 PM CDT Monday may 20 2013
Widely scattered showers will be possible through the overnight
hours as a low pressure center moves into the area. Ceilings will
degrade to MVFR at Minnesota sites...with IFR ceilings at kaxn-kstc-krwf in
closer proximity to the low pressure center. Ceilings gradually
scatter and improve by 18z Tuesday. Scattered showers/ts will be
possible again on Tuesday. Winds will become southwest/westerly on
Tuesday at all but kaxn/kstc where northeasterly winds will
persist.
Kmsp...
after the line of showers and thunderstorms exits msp /by
08z/...slight visibility reductions in br will be possible through
sunrise. Ceilings expected to lower to around 1800 feet
overnight...and scatter out for awhile Tuesday afternoon. Southeasterly
winds prevail through the overnight hours...veer to southerly by
daybreak...and then southwest/westerly during the afternoon.
Speeds at 5-10 kts through the period.
/Outlook for kmsp/
Wednesday...VFR/MVFR ceilings with -shra likely. Winds NE at 05g10kts.
Thursday...VFR. Winds north-northeast at 10-15kts.
Friday...VFR. Winds southeast at 5-15kts.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...clf
long term...clf
aviation...ls
