FXUS63 KGRR 052037

Area Forecast Discussion
National Weather Service Grand Rapids MI
337 PM EST Sun Feb 5 2023


.DISCUSSION...(This evening through next Sunday)
Issued at 320 PM EST Sun Feb 5 2023

- Showers and gusty winds Monday Night to Tuesday AM with
  possible mix/ZR near Route 10 Ludington to near Clare

A cold front will be tracking  eastward through the region during
this time. As surge of moisture from the Gulf will advect into
this frontal zone as it moves in. The associated mid level vort
max will also be digging in...so decent lift is possible. The GFS
does show some negative showalter values and the HRRR does
indicate some CAPE as well. Thus we could end up with convective
showers pushing through during this time. We did not add thunder
to the forecast yet as not all models show instability. We will
maintain the high POPs though. With a strong low level jet
accompanying the passage of this system...gusty winds are
expected. Most indications are that 30 to 40 mph values are likely
to occur...but the GFS ensemble values are topping 40 mph.  The
soundings support liquid precipitation for most of the area.
However...for interior Lower MI...surface temperatures will be
near freezing...so we will need to monitor the potential for
possible icing. The main risk window for wintry impacts is from
06z to 14z Tue.

- Close call for mixed precipitation Thu into Thu night

The pattern has become a little more favorable for at least a
period of mixed precipitation for interior parts of Lower MI. High
pressure over Ontario will generate northeast winds that will
funnel down some colder air from that region Thursday. At the same
time low pressure will be tracking into Lower MI. Enough cold air
looks present to support at least a period of mixed precipitation.
The relatively warmer air associated with the storm moving in is
expected result in mainly a rain event. However with the northeast
zones being the coldest...the potential impact risk is the highest
there. The precipitation will be steady and possibly heavy at
times. The PWAT values are highly anomalous for this time of the
year. A coupled upper level jet is noted Thursday which will allow
for stronger upper level divergence. A strengthening warm front
along with a 40 to 50 knot LLJ crossing it supports the stronger
low level lift. As a result of all this...there is an increased
potential for more than an inch of qpf from this storm system for
Grand Rapids. This is supported by the 24 hr ensemble qpf trends
from most of the models.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1245 PM EST Sun Feb 5 2023

The cold front will track through the TAF sites this
afternoon...mainly dry. MVFR clouds were developing along and
behind the front. Thus impacts are expected. Gusty wind
occasionally topping 20 knots are likely to occur as we...but
the winds will decrease tonight as the pressure gradient weakens.
The low levels gradually dry out tonight and into Monday. This
will support conditions becoming VFR.


Issued at 320 PM EST Sun Feb 5 2023

The winds and waves have diminished under criteria for small craft
conditions. Thus we cancelled the advisory. Another marine
headline will be needed for Monday night into Tuesday as the next
front tracks into the marine zones. This system will feature a 50
knot low level jet. The mixing height will be limited though. Most
models show small craft conditions to dominate in this
period...but several models like the GFS and the HRRR are
suggesting gales.





NWS GRR Office Area Forecast Discussion