Area Forecast Discussion

FXUS63 KGRR 181920
Area Forecast Discussion
National Weather Service Grand Rapids MI
220 PM EST Sun Nov 18 2018
Issued at 220 PM EST Sun Nov 18 2018
Highlights of the forecast (and any associated changes from
previous forecast packages) are noted below:
- Two clipper systems will impact Lower Michigan: Monday afternoon 
and evening (faster than previous forecast packages) and Tuesday 
night. While both have the potential to produce a quick dusting to 
half inch of snow mainly west of US-131, potential impacts continue 
to look minor. 
- Warmer temperatures are expected Friday and Saturday with rain 
chances increasing Friday night (also faster than previous forecast 
package but definitely not set in stone).
.DISCUSSION...(This evening through next Sunday)
Issued at 220 PM EST Sun Nov 18 2018
Fairly quiet conditions have taken hold across Lower Michigan owing 
to a northeastward branch of a large high pressure system centered 
over the Central Plains extending toward the Great Lakes. Broken 
lake effect cloud cover is scattering as of this writing owing to 
increasing subsidence associated with the aforementioned high 
pressure system and decreasing low-level moisture. Temperatures are 
in the low to mid 30s, warmest toward the Indiana border, which is 
still ~10 degrees below normal for this time of year.  So, there's 
not a whole lot going on outside the window right now.
The greatest concern (which admittedly is not that high) remains on 
the two clipper systems expected to move through the Great Lakes 
tomorrow afternoon through early Wednesday morning.  Interestingly 
model guidance has "flipped" the two systems, with the second now 
looking stronger than the first, but the impacts still appear 
limited. Monday afternoon and evening, a cold front will sweep 
through the lower Great Lakes with an associated region of light 
snow. Note that the arrival of the system is faster in this 
forecast package than those previous, with precipitation starting 
north of I-96 perhaps as early as 18Z/1PM EST. Forecast thermal 
profiles suggest that rain may mix with snow at the very onset of 
the precipitation owing to a shallow (~500 ft) above-freezing 
layer, but predominantly snow is expected especially behind the 
front. A few bursts of moderate snow are also possible owing to 
modest lift through the DGZ, but the progressive nature to the 
system will limit accumulations to a half inch or less. The 
"heaviest" should fall west of US-131 where modest lake 
enhancement is possible. 
The second system will swing through late Tuesday night and into 
Wednesday morning with slightly better forcing (e.g. the low will 
actually be deepening as it tracks from the U.P. of Michigan toward 
Lake Huron). However, the available moisture looks shallow and 
largely below the DGZ suggesting that again, snow accumulations will 
be limited to a half inch or less (mainly west of US-131). We'll 
have to keep an eye on the potential for a burst of lake effect 
snow within west wind belts along the backside of the second 
system before sunrise Wednesday, but rapidly decreasing low-level 
moisture may keep such a threat minimal. Travelers are still 
encouraged to stay up to date on the forecast especially if 
planning to travel to the northern lower peninsula where more 
meaningful snow accumulations are possible. 
As for the extended period...Wednesday night looks chilly with 
area wide lows in the teens and wind chills approaching the single
digits. Thanksgiving continues to look dry and cool with highs in
the 30s and broken sunshine during the afternoon/evening hours. 
Not much has changed in the thinking for the end of next week with
warmer temperatures in the mid to upper 40s Friday and Saturday 
though rain chances may be highest Friday night and into Saturday 
instead of later (e.g. timing is a bit faster with this forecast 
package). Additionally, we're still eyeing a return to winter next
week with cooler temperatures and periodic chances for frozen 
.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1216 PM EST Sun Nov 18 2018
A deck of scattered to broken lake effect clouds rooted at
2500-3000 ft and in which light to moderate icing is possible will
persist at all TAF sites through the daylight hours before clouds
clear tonight. Patchy BR is possible overnight at AZO/BTL/LAN but
otherwise VFR conditions are expected to prevail through the end 
of the TAF period. 
Issued at 220 PM EST Sun Nov 18 2018
Marginally hazardous conditions for small crafts due to waves near 3-
4 ft will continue this afternoon mainly north of Little Point Sable 
before subsiding toward midnight tonight.  A small window of 
hazardous conditions for small crafts is possible tomorrow afternoon 
from Muskegon south to Saugatuck with waves in the 3.5-4.5 ft range 
from 16Z/11AM to 00Z/7PM EST. Waves will then increase near the 
Points Monday night lasting into daylight hours Tuesday morning, 
before hazardous conditions for small crafts expand across all of
eastern Lake Michigan Tuesday night through Wednesday night. 
Issued at 220 PM EST Sun Nov 18 2018
There are no hydrologic concerns through next weekend. Several 
rounds of light snow and rain will occur through Tuesday night, but 
amounts will be light. Longer range models are suggesting a few 
rounds of rainfall will occur during the Friday night through Sunday 
timeframe, but we don't have confidence on the timing of these 
rounds yet. At this time, rainfall does not look heavy enough to 
cause notable impacts to river levels.
Well below normal temperatures will persist through midweek, however 
the threat for ice jams remains near zero as daily average 
temperatures remain above 20 degrees. Warmer weather is expected 
towards the end of next week.
LM...Small Craft Advisory until midnight EST tonight for LMZ849.