NWS Forecast Discussion

Below is the latest Area Forecast Discussion from the Twin Cities National Weather Service office in Chanhassen, MN. It gives insight into why the forecasters are making the predictions you read in your local forecast. The overall "big picture" of the atmospheric setup is well described, as well as the forecasters' interpretation of the various Computer Atmospheric Models (CAMs). Sometimes, very specific information is available here that is not available, or otherwise generalized, in the public forecast.

000
FXUS63 KMPX 271154
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
654 AM CDT Sat Apr 27 2024

.KEY MESSAGES...

- Today will be dry, but a cool rainy day is on tap for Sunday.

- Another round of showers and thunderstorms likely on Tuesday,
  with a few stronger storms possible.

- Rest of next week looks generally dry with seasonable temperatures.

&&

.DISCUSSION...
Issued at 344 AM CDT Sat Apr 27 2024

Surface low this morning is moving across southern MN and is on its
way to central Lake Superior by the afternoon. A PV boot has
rotated around the surface low. PVA ahead of this PV anomaly is
driving the shield of rain across central MN early this morning,
but subsidence and dry mid level air behind the leading edge of
the PV anomaly has quickly cut off the precip over southern MN.
Given the track of the low, we`re still on tap for a dry
Saturday as the low and PV anomaly move northeast of the MPX
area. We`ll be on the cool side of any front, which necessitated
another downward nudge on highs today. We went closer to the
CONSraw guidance, which came in between the 25th and 50th NBM
percentile with the cloudy and post frontal airmass expected.

For the Sunday system, we`ve seen a slower trend with this system.
As a result, we reduced PoPs quite a bit for tonight, then took a
good hit out of highs for Sunday. The low now looks to remain to our
south through the day on Sunday, with Sunday looking rather raw now,
with temperatures struggling to hit just 50 along and north of a
line front Redwood Falls, to the Twin Cities and Ladysmith with a
steady rain expected as well. Great sleeping weather if you happen
to be working the overnight shift! As for the severe risk, given the
slower and further southeast track of the surface low expected,
severe chances in the MPX area are looking pretty low, with the
better severe risk on Sunday across northeast Iowa toward La Crosse.
Instead, it will be another day on the cool side of the front, with
maybe an isolated storm being possible in our widespread rain.

We dry out and have another cool, post frontal day on Monday, but
that will be short-lived. Models have really started to round into
agreement on our next system coming in on Tuesday. This shortwave is
looking stronger, with the exit region of a jet streak moving in as
well to aid in the development of showers and thunderstorms. The
NBM has bumped PoPs up to the likely category. The forcing will line
up with peak heating, so we`ll take on a more convective nature to
the activity on Tuesday. Instability looks to be lacking to drive a
significant severe threat, but given the wind profiles, this looks
to be an environment that could support a few marginally severe
storms.

For the rest of the week, we`ll have a WSW jet overhead with a
positively tilted trough extending from an h5 low in northwest
Ontario back toward eastern MT. This will keep temperatures
seasonable for the rest of the period. It is also one where there`s
little agreement in the ensembles on any periods that will be
completely dry. This results in the endless PoPs we have in the 20s
after Tuesday. Though it should be said, our climatology for PoPs
this time of year is up in the mid 30s (ie. any day during the last
week of April has seen measurable precip 35% of the time), so these
low PoPs are actually saying our chances for rain are below normal
for the rest of the period after Tuesday. Given the flow, we`ll
probably manage to squeeze a little precip out of any passing wave
in the jet stream, though at this point, there is little agreement
on when we may see one of those passing waves, so you get a forecast
that gives the impression it will be wetter than it will be in
reality.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 640 AM CDT Sat Apr 27 2024

Surface low is currently located in the northwest TC metro,
with any lingering light rain confined to the north and west of
the low. By 16z, ra/dz is expected to be done for all MPX
terminals, with dry weather persisting until rain moves back in
Sunday morning. Cigs will be lowest over the next couple of
hours as the low moves through the region. After that, we`ll see
gradual improvements in cigs through the day. The idea of a
period of VFR cigs developing this evening between these two
systems still looks possible, though it certainly wouldn`t be a
surprise to see MVFR cigs remain locked in through this period.

KMSP...Until the surface low moves out of the metro, we`ll
continue to see vis reductions with some -DZ and IFR cigs. As
the low moves out later this morning, improvements will
commence quickly between 16z and 18z. Given the slowing trend
with the Sunday system, followed the slower timing we`re seeing
with the next round of rain holding off at MSP until after 12z
Sunday.

/OUTLOOK FOR KMSP/
SUN...MVFR/IFR with -RA. Wind ENE 15-20G25-30 kts.
MON...MVFR/-SHRA early, then VFR. Wind WSW 15-20G30 kts.
TUE...VFR. Chance aftn MVFR/-TSRA. Wind SW bcmg NW 10-15 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.

&&

$$

DISCUSSION...MPG
AVIATION...MPG

NWS MPX Office Area Forecast Discussion