Wednesday: Mostly cloudy. Afternoon highs in the low-to-mid-80s.

Thursday: Some spotty convective thunderstorms possible, particularly in Pennsylvania, with scattered light rain showers elsewhere. Early low temperatures in the low 60s; afternoon highs in the mid-80s.

Friday: Some spotty convective thunderstorms possible, particularly in Pennsylvania, with scattered light rain showers elsewhere. Early low temperatures in the low 60s; afternoon highs in the mid-80s.

Saturday: Drier; mix of sun and clouds. Early low temperatures in the low 60s; afternoon highs in the mid-80s.

Sunday through Tuesday: The models are in general agreement that a cold front is coming. It’s not a particularly strong front as far as temperatures (don’t worry, winter isn’t coming yet); in fact, temperatures will only drop into the upper 70s at the lowest for highs, and the cooldown should help stabilize the atmosphere after Monday. Sunday, however, people in the region can expect some heavier rain to come through, and highs in the low 80s. The MOS ensemble is in strong consensus that by next Wednesday, high temperatures could be as low as the low-to-mid-70s, a welcome relief from the warm and sticky summer the region has experienced so far.

I’m cutting short at 8 days today. Yeah, I know, I usually do 10– so sue me.

~J.M. Fuller

Through Thursday Night
Although surface dewpoints have fallen slightly behind the first front, there is still plenty of moisture around in the lower atmosphere waiting to be converted into clouds and rain. A developing Lake Erie breeze once again this afternoon could be enough convergence to spark an isolated thunderstorm. Due to the very isolated nature, no need to advertise the threat too much in the forecast. Better overall dynamics arrive around sunset so PoPs will be bumped up for later this evening.

After midnight, things will begin to dry out as everything shifts east.

Friday
By sunup, we will see a fair amount of “un-hazy” sunshine making a return to Rochester. The feel on Friday will be significantly different than prior days this week as much drier air will spill down from Canada. In addition, highs on Friday will struggle to make it into the mid 70s.

As noted above, a third front may generate a few light showers Friday evening, especially south and west of town. If you have any outdoor activities, they should be fine. Only a few sprinkles possible.

Saturday/Sunday/Monday
A large area of high pressure will set up camp over the Great Lakes beginning on Saturday with no worries of any showers or thunderstorms during this time period. The only thing to worry about are overnight lows Friday and Saturday night. Away from the lake and urban areas, overnight lows will drop well into the lower 50s with some locations south of the Thruway seeing 40s. It’s getting to the time of the year now where cool nights and warm days will be common.

Starting tomorrow, conditions will be noticeably different. Temperatures will be cooler and dewpoints will drop all the way down to near 50°. The wind direction will be different as well. Expect a cool breeze from the northwest rather than a hot and sticky breeze from the south. These dry and quiet conditions will last right through the weekend where conditions could not be better! An abundance of sunshine is expected this weekend with comfortable highs in the mid 70s on Saturday and into the low 80s on Sunday.

Stay dry today and enjoy the upcoming weekend!

TE

Tuesday
First, the easy call. With partly to mostly sunny skies and 850mb temps of around 16°c, highs in the mid to upper 80s is as easy as it gets. As for precipitation potential, that’s the challenging issue at hand. We have plenty of moisture in the air and daytime heating will lead to some instability in the air, but finding a trigger will be the final ingredient we’ll need to develop any isolated thunderstorms. On Monday, the eastern edge of the Lake Erie breeze served as a focal point for yesterday’s scattered showers and storms. With winds a little more southerly today, I don’t think it will reach the Rochester area. With that said, the best chance for a trigger will be from oragraphical influences across the Southern Tier and Finger Lakes region so best chances will be south and east of Rochester. Any activity will quickly wane this evening with the loss of daytime heating. A warm and muggy night ahead.

Wednesday
Pretty much the same story for Wednesday as above. 850s a couple of degrees warmer ranging from 18°-20°c so expect highs on Wednesday to be a couple of degrees warmer as well. With the cold front well to our northwest, still looking for a source of lift. Best chance again will be from a Lake Breeze or from differentials in terrain. Nearly impossible to fine tune exact locations at this time.

Thursday
Our focus turns towards the approaching cold front with models wanting to bring it through Thursday morning. If this is the case, we can expect just a few showers during the morning. If the front slows down a bit, we could be in for a few hefty thunderstorms on Thursday. Either way, we’ll see something out of this front. I’ll work the details out in the graphical forecasts above when the time comes.

Long Term
Surface high pressure builds for Friday and the weekend. Looks like a great forecast with plenty of sunshine, low humidity, and temperatures around 80° for Friday, Saturday, and Sunday. There are no huge indications of any big heat building during the next 5-7 days.

Tuesday: Mostly sunny. High temperatures in the upper 70s.

Wednesday: Mostly sunny, slightly warmer. Early low temperatures in the upper 50s, slightly cooler in the valleys. High temperatures in the low 80s.

Thursday: Rain in the  overnight; clouds and sun by daylight. Lows in the low 60s. Highs in the mid-70s. Lows heading into Friday morning in the low 50s.

Friday through Monday: Friday and Saturday look to be dry, mostly sunny and comparatively cool. Afternoon highs for those days will likely hover around 70, possibly in the low 70s. Low temperatures will be around 50. As Cattaraugus County Fair week approaches, the models are suggesting an increased chance of precipitation but a slight bump in high temperatures into the mid-70s. This is associated with a wind shift that will bring warmer, more moist Gulf air over the region. It won’t be hot and sticky like the past couple of weeks, but it’ll raise the threat of convective thunderstorms (it does not appear to be an organized front).

Long range: GFS pushes a body of fairly (i.e. easily more than half an inch) heavy rain across the Great Plains (quite quickly) into the area on Wednesday, August 4.

Climatologically speaking: The slide begins. As I stated in a previous post, July 22 is the day of peak temperature, climatologically speaking, in Little Valley. As the days begin to get shorter and shorter, less daylight, and less direct daylight, begin to lead temperatures downward. It doesn’t begin to have significant effect until August, but as far as high temperatures go, it’s (generally) all downhill from here. We notice that with the beginning appearances of cold fronts this week. This doesn’t rule out more hot days like we’ve seen earlier this summer, but they will be fewer and farther between as August progresses.

These thunderstorms are sandwiched between the Lake Erie lake breeze and the Lake Ontario lake breeze. These two colliding breezes show up beautifully on satellite imagery as the low level flow is indicated by the yellow arrows in the image. This convergence in addition to the already warm and soupy airmass already in place, was more than what was needed to get things firing.

As the evening wears on, this area of activity will die down as both lake breezes fizzle out; however, we still have a cold front on our doorstep that may develop more thunderstorms a little later this evening. Could see more strong winds and heavy downpours.

In other news, I’ll be out of town beginning tomorrow morning until Sunday evening so I’ll be unable to update any of the forecasts.

Tuesday night into Wednesday: Mostly cloudy. A chance of some scattered showers in a few places, but these will likely be very sporadic. Early lows in the low 60s. Afternoon high temperatures in the upper 70s.

Thursday: Mostly cloudy for the overnight, with clouds breaking and partly sunny skies during the day. Early low temperatures in the upper 50s. Afternoon high temperatures around 80.

Friday through Monday: Rain comes in as the core of a low pressure mass moves across the northern plains and reaches the Twin Tiers on Friday. It will likely continue to bring precipitation through Saturday. The two models seem to disagree over whether or not the bulk of the rain will be on Friday (as the NAM suggests) or if a second wave of precipitation will push through on Saturday night (as the GFS suggests). Either way, the sum total of precipitation should be between 0.5″ and 1.0″. High pressure is expected to push back into the area for Sunday and Monday. In regard to temperatures, they should remain fairly steady, with low temperatures in the low 60s and high temperatures in the low 80s.

Long range: The outlook for July 27-29 looks much like the two days preceding it; high pressure will likely remain in place through that time period and temperatures will likely remain fairly steady.

~J.M. Fuller

Sunday Night
Radars upstream of us over the upper Great Lakes show plenty of on going showers and thunderstorms as of Sunday afternoon. They should hold together as the move to the east and will be on our doorstep after dark. A few weak showers are out ahead of this activity, so a passing sprinkle or two is possible for the remainder of Sunday.

Monday
Monday will be an active day with passing showers and thunderstorms, especially before 3pm. There may even be some clearing by early evening. Temperatures will mainly in the upper 70s.

Tuesday
Partly to mostly sunny skies during the morning will give way to increasing clouds, similar to the day on Sunday. May even see a few showers by late afternoon on Tuesday. Highs in the upper 70s again.

Wednesday/Thursday
High pressure begins to build on Wednesday leaving us with mostly sunny skies, low humidity, and comfortable temperatures right around 80. Same forecast for Thursday, but a degree or two warmer.

Anyways, the weather setup as of midday Thursday looks like this. A low pressure system over extreme north western Ontario is moving southeast, but will still remain well to our north. Its associated warm/cold front will both cross our area over the next 24-30 hours or so. In fact, based on current surface conditions, it looks like the warm front has already lifted north of Lake Ontario. Temperatures and dew points are both climbing leading to a warm and sticky afternoon. With the cold to our west (Chicago area now), it will be a warm and muggy night heading into Friday.

On Friday, the “cold” front will move through, but temperatures on each side of the boundary are not significantly different; however, dew points are much lower behind it. With the passage of the front, showers and thunderstorms can be expected on Friday, mainly during the morning to early afternoon. Will need to keep an eye out for a few more slow moving thunderstorms, especially with all of the recent rainfall. Flooding could be a concern.

Friday
Showers and thunderstorms will be crossing the area. The best window for this activity will be between 7am and 2pm. Again, a few storms will be capable of dropping an inch or two of rain in a short period of time. Look for an evening high in the mid 80s as I think we might break out into partly to mostly sunny skies for the late afternoon.

Saturday
On Saturday, just a small chance of an afternoon shower or thunderstorm. The models show a weak front dropping south and cannot rule out a wayward storm or two developing. Not everyone will get in on this action though. Otherwise, temperatures will climb back into the mid to upper 80s.

Sunday
And finally, for Sunday, expect mostly sunny skies. Temperatures will be within a few degrees of 90.

Now, as for the Twin Tiers Ten-Day Forecast…

The National Weather Service has issued a Flash Flood Warning for portions of Allegany County around and east of Rushford, due to heavy downpours.

Tuesday: Mostly cloudy, with isolated convective thunderstorms. Afternoon highs in the upper 70s.
Wednesday: A few scattered showers possible, but unlikely, in the overnight hours, then skies clearing in the afternoon. Early lows in the low 60s. Afternoon highs in the low 80s.
Thursday: A clear, calm, cool night, followed by a hot, hazy day. Early lows in the low 50s in the valleys, upper 50s elsewhere. Afternoon highs in the upper 80s. Winds shift into a southerly direction.

Friday through Monday: GFS is forecasting a low to move well to our north but bring a weak “cold” front across the region on Friday, with the possibility of precipitation. Gulf moisture becomes the bigger threat for Saturday as a weak southwesterly flow pushes a separate body of light rain into the area. Sunday, on the other hand, should be dry, as should Monday. Low temperatures are likely to remain in the low 60s throughout the period, but high temperatures will hit the low 80s on Friday before dropping into the upper 70s from Saturday through Monday. In PA regions, where the southerly wet flow should remain more dominant, temperatures could easily remain in the low 80s.

Long range: Both the GFS and the ECMWF forecast the jet stream to establish a zonal flow over the region in the 8-10 day forecast period. GFS forecasts a surface low pressure system to work its way into the jet and swing its way over the area on Tuesday or Wednesday. It’s too far out to predict how much precipitation it can produce, but it’s a fair guess to say it will be significant. Temperatures should remain fairly steady in the low 80s.

Mid-July is, climatologically speaking, the hottest month on the calendar in the western New York/Twin Tiers region. It is also the one where high temperatures are relatively stable. The average high temperature for the Little Valley station is 78 for every day between July 5 and August 5, with the exception of July 22, which peaks at 79.