FXUS63 KGRR 191929

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 PM EDT Sun Sep 19 2021


Issued at 328 PM EDT Sun Sep 19 2021

- Upper Troughing Moves East with Heavy Rain Tuesday and showers
  lingering into Thursday


.DISCUSSION...(This evening through next Sunday)
Issued at 328 PM EDT Sun Sep 19 2021

There is better forecast confidence today in the details as
models are converging towards the sharp trough axis cutting off
into an upper low and troughing persisting across the Great Lakes
region through the end of the week.

We have been watching Gulf moisture that is the remnants of a
tropical cyclone slowly moving northward the past couple days. A
line of showers and thunderstorms across southern Indiana this
afternoon mark the leading edge and the CAMs forecast showers to
reach southern Lower Michigan Monday morning and spread north
across the forecast area by afternoon. Coverage is expected to be
less than currently seen, but precipitable water values spike up
to over 1.5 inches by late afternoon and heavy rainfall rates are
possible with any deep updrafts. SHear profiles are weak and
severe weather threat is low.

Surface cold front plods across the forecast area from west to
east on Thursday morning and afternoon. We expect basin average
rainfall of around an inch with some 2 inch amounts possible
across the southeast forecast area. Rivers should be able to
handle this as they are near their lowest levels of the year.

Upper low lingers on Thursday with scattered showers and
temperatures stuck in the 50s as much cooler air is drown south
and clouds and showers prevent much in the way of warming. The
upper low departs by the weekend with generally fair but cool
weather through Sunday.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 128 PM EDT Sun Sep 19 2021

VFR conditions prevail through tonight then MVFR conditions spread
north into Lower Michigan as southerly winds bring Gulf moisture
and increasing chances of showers later Monday. Southeast winds
around 5 to 10 knots today go south on Monday with some gusts over
20 knots.


Issued at 328 PM EDT Sun Sep 19 2021

South winds ramp up on Monday with gales expected north of
Holland by Monday evening, so we will have a Gale Warning for that
area into Tuesday morning. There could be a lull Tuesday afternoon
but winds and waves may be hazardous to small craft through





NWS GRR Office Area Forecast Discussion