Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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404 FXUS63 KGRR 211325 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 925 AM EDT Sat Sep 21 2024 .KEY MESSAGES... - Dense fog early this morning, then sunny and hot today - Showers and scattered storms Sunday - Starting Monday, a week of near to above-normal temperatures, and a chance of showers/storms on Tuesday && .UPDATE... Issued at 924 AM EDT Sat Sep 21 2024 Fog is dissipating or lifting into low stratus, which will also be mixing out in the next hour or two. The Dense Fog advisory has been cancelled. && .DISCUSSION... Issued at 332 AM EDT Sat Sep 21 2024 - Dense fog early this morning, then sunny and hot today Surface obs show widespread dense fog with vsbys aob 1/4sm early this morning. A Dense Fog Advisory is in effect until 10am; fog will slowly burn off this morning, leading to a sunny day. H8 temps climb to 18c this afternoon which will lead to surface temps in the mid 80s...roughly a dozen degrees above normal. Humidity this afternoon will be somewhat mitigated by mixing down some drier air from aloft, which will send dewpoints into the 50s. - Showers and scattered storms Sunday An upper trough will move across southern Canada today and Sunday and push a cold front through the region. Most of the dynamics with this system will remain well north of the cwa. However, there will be a strong push of moisture with it...precipitable water values jump to around 2 inches Sunday thanks to a 40 kt LLJ. Instability will be lacking though; MUCAPE is a few hundred joules at best. Mid level lapse rates are only around 5c/km, which is not impressive. Thus, most of the precipitation will be showers and perhaps isolated storms. QPF could range from a half inch to over an inch, which would be welcome to an area that hasn`t seen much rain lately. - Starting Monday, a week of near to above-normal temperatures, and a chance of showers/storms on Tuesday Temperature-wise next week, while there remains a fair amount of spread among the ensembles in the day-to-day temperatures (depending on a complex evolution of the upper-level wave pattern), the median of the solutions are pointing to temperatures closer to normal early in the week, then warming up a little later in the week. This is a break from the abnormally long stretch of 80-degree weather that occurred in mid-September. Normal highs/lows for this time of year are on their way to about 70/50 this time of year. Daily rain chances have been a challenge to predict for the upcoming week. Ensemble systems and their constituent members have provided a wide range of plausible rain outcomes: ranging between a mostly dry week, to a somewhat showery week, to a one-or-two episode heavy rain threat. Adding to that are run-to-run inconsistencies among each of the ensembles. This can be forgiven since the interaction and evolution of the wave patterns between the northern-stream polar jet and the southern-stream subtropical jet is set to be rather chaotic. After Sunday, the best chance of rain still appears to be Tuesday as the southern-stream low out of the Desert Southwest becomes incorporated into the northern stream as it moves over the Great Lakes. However, the CMC ensemble is much less enthusiastic about Tuesday, and there are still a portion of members among the GFS and ECMWF ensemble that stay dry too. Outlier solutions on the rainy side indicate the potential for over an inch of rain in spots on Tue. The chance of rain is relatively higher in southern locations. Later in the week, models have been tending to develop cut-off lows between the northern and southern jets over or near the Great Lakes region. Where a cut-off low might form will dictate whether late week is dry or has a rain episode. In the latest run of the ensembles, there is a cluster of solutions that offers a chance of a soaking rain on Friday, but this cluster is in the minority. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 703 AM EDT Sat Sep 21 2024 Ceilings/visibility at or below minimums presently due to fog at most airports. AZO and BTL fog has been more patchy, so flight conditions there could change dramatically for a short amount of time. Models and past experience this week suggests gradual improvement in conditions after 13Z but LIFR to IFR may hold on at some locations until 15 Z. After 15 Z, VFR is likely for the remainder of the day. && .MARINE... Issued at 332 AM EDT Sat Sep 21 2024 Low wave heights expected today, but they`re likely to increase later Sunday into Monday as north winds develop behind a cold front. Two to four foot waves will be common during this time period but conditions will probably be just under Small Craft Advisory criteria. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ UPDATE...Ostuno DISCUSSION...04/CAS AVIATION...CAS MARINE...04