518
FXUS63 KMQT 070838
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
438 AM EDT Tue May 7 2024

.KEY MESSAGES...

- An approaching low pressure system brings a line of showers
  northward into the U.P. this afternoon. Breezy southeast winds
  are also expected today, gusting up to 25-35 mph with stronger
  winds in the west.
- A brief period of elevated fire weather conditions is possible
  preceding the showers in the northern half of the U.P. except
  for the Keweenaw.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 437 AM EDT Tue May 7 2024

Right now the UP is dry and fairly quiet with light south to
southeast winds. Current RAP analysis shows the mid level ridging
over the Great Lakes that is providing us this quiet period. A
closed low is analyzed over western South Dakota with a shortwave to
its south over Kansas and the Panhandles of Texas and Oklahoma. The
sfc features include a high pressure over northeastern Ontario which
extends into the Lower Great Lakes and two low pressure systems out
over the west. The northern low is the stronger of the two at 981mb
and the second one (which is associated with the shortwave) is
located at 997mb over eastern Kansas. With the high pressure
diminishing as it retreats northward and ridging still holding on
through this morning, dry weather will persist with mild temps in
the 40s (cooler in the east).

Today brings precip back into the forecast. The closed low and
associated sfc low will spin over the Dakotas, slowly weakening.
Meanwhile, the central plains shortwave pivots northeast toward the
UP by this evening. The weaker sfc low will follow a similar path,
occluding as it approaches, ending up over Lake Michigan by the
evening. The occluded front is expected to lift from south to north
this afternoon bringing a line of showers with it. Showers along the
WI/MI state line are expected to begin around 1-2 PM EDT, reaching a
line between Houghton/Marquette/Manistique by around 6 PM EDT, then
the rest of the UP around 7-9 PM EDT. Instability will be lacking as
indicated by the 5/7 0Z HREF MUCAPE with values around 100 j/kg over
the south central. Also bulk shear and lapse rates will low around
20-35 kts and 6C/km respectively. Given the set up, strong
thunderstorms can be ruled out, but a few rumbles of thunder are
possible in the south and along the WI/MI state line.

Ahead of the showers, some mixing is expected to bring some lower
RHs and breezy southeast winds. Highs will occur earlier in the
afternoon in the south due to the front lifting in. Highs in the 60s
are expected with upper 50s near the lakeshores; warmer temps hold
on longer in the eastern UP. The brief period of mixing ahead of
precip will result in lower RHs dipping into the 20s to low 30s in
the northern half of the UP save for the Keweenaw. Gusty southeast
winds up to 20-30 mph with a few gusts to 35 mph possible over the
far west and in the Keweenaw will also be a fire weather concern.
That said, this period of elevated fire weather conditions will only
last 3 to 6 hours and anticipated precip will bring some relief with
a few hundreths to 0.35" of rain; areas in the south central UP may
see up to 0.5-0.75" by this evening. With the uncertainty on the
duration of elevated fire weather conditions and the period being
brief to begin with, no SPS was issued.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 344 PM EDT Mon May 6 2024

The extended forecast is largely dominated by a trough currently
approaching the Northern Great Plains and its complex evolution and
influence on the surface lows moving across the CONUS through the
upcoming week, which will keep precipitation chances in the forecast
throughout the forecast period.

For Tuesday, the negatively tilted trough forms a closed off low
over the Northern Plains as the shortwave continues northeast from
Iowa to the Upper Great Lakes. This stacked low will be stalled over
the Dakotas Tuesday through Wednesday morning, but a shortwave
rotating around the base of the low aloft will be the focus for the
weather pattern heading into the midweek. This shortwave will get
jet support as it becomes coincident with a right-entrance region of
a ~125 kt 300mb, giving enough synoptic support for showers over the
UP beginning Tuesday late-morning in the west and overspreading the
UP by the end of the day. This continues a model trend of
precipitation arriving later with each major model run. With bulk
shear low (20-35 kts) and mean 12Z HREF MUCAPE of around 100mb, not
many thunderstorms are expected, but a few rumbles of thunder can`t
be ruled out. With moisture advecting in and cloud cover ahead
limiting mixing potential, minimum RHs barely fall into the 30s
ahead of the approaching showers, so fire weather shouldn`t be a
concern, and with a WPC Marginal Risk of Excessive Rainfall, any
minor fires that may start should be extinguished naturally.

The pressure falls associated with the shower activity Tuesday will
become a discrete surface low pressure by Wednesday morning and
depart the region by the afternoon. As it does, the original closed
low over the Dakotas will weaken from a peak strength of near 980mb
Tuesday morning to near 1000mb by midday Wednesday as it slides
southeast. As it does, it will phase with another weak lee cyclone
off the Rockies, with ensembles tracking this new low generally
around Lake Michigan and Illinois by overnight Wednesday into
Thursday. Precip will be the forecast if the northern clusters
verify, but the UP could be high and dry if a more southern solution
materializes. By Friday, anomalous ridging over coastal British
Columbia will be contrasted with anomalous troughing over the Lower
Great Lakes, putting the UP in a northwesterly flow regime. Some
deterministic and ensemble guidance suggests a clipper-type low late
in the week into the weekend, keep PoPs in the forecast, though
uncertainty is high in any specifics as the complex setup has a lot
of variables to work out first. Confidence is increasing that this
ridge will shift over the Great Lakes by the midweek of next week,
warranting the CPC to favor below normal precipitation for the
second half of May.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 121 AM EDT Tue May 7 2024

As an occluding front approaches from the south today, expect LLWS
to fire up over KIWD at 06z this morning, continuing until the mid-
morning hours. Otherwise, the VFR conditions deteriorate this
afternoon as rain showers along the occluding front move over the
area from southwest to northeast. As we move into the overnight
hours, expect the conditions to worsen down to LIFR/IFR across the
TAF sites. While LLWS could be seen at all of the TAF sites during
the daylight hours into the early evening hours today, given that
some mixing is expected in the boundary layer to the end of the TAF
period, no LLWS is expected. However, should there be breaks in the
mixing during the daylight and evening hours, expect LLWS across the
terminals during those breaks.

&&

.MARINE...
Issued at 344 PM EDT Mon May 6 2024

With high pressure over the Upper Great Lakes, resulting stability
will keep winds mainly below 20 kts through tonight for the vast
majority of Lake Superior. The exception to this would be over the
far western portion of the lake near the Duluth Harbor where some
northeast channeling may yield some gusts up to 25 kts. An
approaching low pressure Tuesday morning will force northeasterly to
east winds to funnel over the western half of Lake Superior to 25
kts by noon Tuesday with a few gusts to 30 kts in the far west and
along the Minnesota shorelines. Winds across the east half of the
lake increase to around 20-25 kts Tuesday afternoon. A brief break
in 20+ kt winds is expected Tuesday night. Periodic chances for
winds in the 20-30 kt range dot the forecast through Thursday as
multiple weak low pressure systems pass through the Upper Great
Lakes region, but uncertainty still remains.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...Jablonski
LONG TERM...GS
AVIATION...TAP
MARINE...GS