166
FXUS63 KMQT 162315
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
715 PM EDT Mon Sep 16 2024

.KEY MESSAGES...

- Isolated to scattered showers and non-severe thunderstorms
  into early evening over western Upper MI eastward to
  Marquette County.

- Extended stretch of well above normal temperatures continues through
  at least Saturday with highs mainly in the upper 70s and 80s.

- Next credible chances of precipitation arrive Friday into the
  weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 402 PM EDT Mon Sep 16 2024

Evidence of a subtle shortwave riding up the backside of a broad
amplified ridge over the Great Lakes combined with PWATs nearly 1.5
or 175-180% of normal and MLCAPE values around 1500 j/kg have led to
the initiation of scattered showers and thunderstorms over western
Gogebic and northern Ontonagon counties this afternoon where the
axis of best instability and theta-e ridging is situated. Coverage
of showers at this time are more isolated to the north and east into
the Keweenaw, southern Houghton, Baraga and western Marquette
counties. Expect this isolated to scattered convection to continue
into the early evening hours over the west and north central
portions of the U.P. before diminishing with the loss of diurnal
instability. No severe storms are expected as deep layer shear is
weak across the area, but the high PWAT values could lead to
torrential downpours with the storms. The unseasonably warm
temperatures have continued today with afternoon readings generally
well into the 80s, except a touch cooler (upper 70s) southeast and
across the Keweenaw Peninsula where lake breezes have kicked in. For
the second straight day we broke a record high temperature at the
NWS Marquette office, reaching 86F thus far today. The old record
high was 82F set in 2017 and tied again in 2018.

Tonight, after showers die off over the west and north central
sections this evening, models indicate quiet and dry weather the
rest of the night. There is a concern that patchy fog could develop
later tonight as we radiate through lower to mid 60s dew points with
probably the best chances for fog south central and southeast where
respective winds are lighter and where dew points near Lake Michigan
and the Bay of Green Bay will be higher (mid 60s). A light southerly
gradient wind flow west and along Lake Superior will likely limit
fog formation there. Expect min temps ranging from the mid 50s
well inland to the mid 60s along the Lake Superior shoreline.

&&

.LONG TERM /TUESDAY THROUGH MONDAY/...
Issued at 319 PM EDT Mon Sep 16 2024

Through the work week, the pattern aloft remains very blocky with a
closed low over the US Southeast through Thursday night. The rex-
block ridge that`s been residing north of the closed low lately will
be replaced by another ridge that will be causing 500mb height
anomalies over northern Ontario to climb to near +30 dam. By Friday,
the low wave number blocked pattern will shift to a high
wavenumber active pattern as the closed low shifts northeast
from under the second ridge, resulting in troughs over the
Eastern Seaboard, the Northern Plains, and over the Desert
Southwest with ridges in between each trough. The surface
weather will reflect this pattern change as the previous dry
conditions and anomalous warmth will be replaced by more
widespread chances of rain into next weekend along with more
seasonable temperatures.

Tuesday looks to be a dry day as the most influential surface
feature remains a 1025mb high centered over New York during the
morning. Global deterministic models show a shortwave passing
through northern Ontario through the day and two of the members of
the HREF (NSSL WRF and FV3 WRF) show precipitation over Isle Royale
and western Lake Superior in response to surface troughing draped
south of the shortwave. Therefore, this forecast will add some
chance (15-26%) PoPs for those areas overnight. With HREF mean
MUCAPE of up to 750 J/kg, an isolated thunderstorm cannot be ruled
out, but severe weather is not expected as shear values of below 20
kt will not allow for updrafts to be organized in a meaningful
fashion.

Despite the erosion of the first ridge aloft over the Great Lakes,
it will be immediately replaced by another ridge moving over from
the Great Plains, resulting in Wednesday and Thursday being another
pair of dry days. Minimum RH values during those days do remain
above critical thresholds, but with wide swaths of the UP going
a full week without rain and nearly all of the UP having less
than a quarter inch of precip over the last week, drying fuels
may be a concern to some fire partners. Thankfully, under the
ridging aloft and with a lack of nearby low pressure centers,
winds remain light, alleviating some of those fire weather
concerns. A few record highs and record warm lows may be under
threat as the NAEFS highlights the near-surface temperatures
above the 90th percentile of its climatology. Lighter winds and
mainly clear skies will provide good setups for radiation fog
each overnight, especially in the south- central, where the Euro
visibility meteograms highlight 20% chances for dense fog.
Leaving just patchy fog in the grids for now until confidence
increases.

As the blocking pattern shifts quickly into a quite active pattern,
troughing will finally arrive from the west late Thursday into
Friday, allowing for higher PoPs to arrive with widespread wetting
rain being likely by the end of the weekend. Model spread is still
high in the details (which is understandable given the increased
number of features to track over the CONUS for next weekend), but
the LREF highlights the western half of the UP as at least
33-66% likely to reach a half inch of rain by the end of the
weekend with the east half with similar probabilities to reach a
quarter inch. NBM high temperatures will also cool behind the
trough with highs closer to normal for this time of year in the
upper 60s and lower 70s.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 714 PM EDT Mon Sep 16 2024

VFR conditions should prevail through the TAF period. A couple of
showers may be in the vicinity of CMX at the very start of the TAF
period but these should quickly dissipate. Patchy shallow fog cannot
totally be ruled out at SAW in the 08-12Z timeframe, but probability
of MVFR or lower is less than 20%. Southerly winds may gust to
around 20 kt at times at IWD/SAW Tuesday afternoon.

&&

.MARINE...
Issued at 319 PM EDT Mon Sep 16 2024

Light winds of 20 knots or less continue over Lake Superior this
week as high pressure ridging over the eastern U.S. influences our
weather pattern for the next several days. Nevertheless, some
showers and thunderstorms are possible tonight and again Tuesday
night as shortwave lows ride along the ridging overtop the Upper
Great Lakes. Chances for 20 kt gusts increase Friday into the
weekend as troughing finally arrives from the west, though details
on the exact track of the surface features are uncertain and will
have a large influence on the details of gusty conditions.

&&

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

&&

$$

SHORT TERM...Voss
LONG TERM...GS
AVIATION...Thompson
MARINE...GS