Bayfield bomber?

General Discussions: ASK John: Bayfield bomber?

By sp123 on Friday, December 05, 2008 - 11:32 pm: Edit Post

looks like the bayfield bomber never really set up is this becuase the winds were to much from the south ? does it matter how fast the wind is from that direction i no the wind was from the southwest most of the day to bad it wasnt a little more westernly would i very light west wind produce mmore snow for the keweenaw. or what is the best overall setup for us here in the keweenaw to get nailed with lake effect?


By admin on Saturday, December 06, 2008 - 07:10 am: Edit Post

It did for a short period Friday morning. I know I got 3" in one hour, but then the winds shifted too much out of the south.

The ideal setup is fairly light winds (5-15 mph) out of the west-southwest.

-John


By frnash on Saturday, December 06, 2008 - 01:46 pm: Edit Post

John, could you 'splain what specific effect lighter vs. greater wind speeds would have on LES generation, compared to 5-15 mph?


By snowfan470 on Saturday, December 06, 2008 - 02:13 pm: Edit Post

Well from what I learned just recently... when wind is to strong in the surface to 850 hPa layer, then the parcel residence time is limited, and the efficiency and production of lake effect snow is limited.
Meaning...the time that a specific bubble of air traveling over the water is limited and has less time in forming lake effect snow bands.
If the wind is too light, land breeze circulations dominate, which prevent steady straight flow of winds over the lake.. preventing intense snow bands from forming.

Does that sound correct John?


By snowfan470 on Saturday, December 06, 2008 - 02:34 pm: Edit Post

Hopefully john doesn't get mad at me for answering that question!


By admin on Saturday, December 06, 2008 - 07:55 pm: Edit Post

frnash-

The explanation snowfan470 gave is part of the story, but in the case of the Bayfield Bomber, the other reason is because the lower wind speeds helps a land breeze to set up. The warmer lake temps cause the air to rise and thus the air is drawn to the lake from the land, which is cold and not causing the air to rise. This lake breeze causes low level convergence of the air just north of the south shore of Superior from around the Porcupine Mountains to where the band makes landfall in the Keweenaw. It is this low level convergence that adds a forcing mechanism to lift the air within the snow band and really gets things cranking. 4-6"/hr snowfall rates are not unheard of with a Bayfield Bomber.

The stronger the natural wind you have, the more the land breeze is negated.

-John


By ubee on Saturday, December 06, 2008 - 08:33 pm: Edit Post

Must be why Birch hill by Ashland hardly gets any snow and Saxon gets dumped on !


By snowfan470 on Saturday, December 06, 2008 - 09:07 pm: Edit Post

Hey john...so isn't what you explained called Thermal Convergence? And also, is the convergence possibly enhanced by the small bay area between bayfield and the porcupine mountains? B/c from what I learned...shallow small bay areas tend to focus the thermal convergence and large deep bay areas such as the southern portion of lake michigan can form meso-vortexes.

Thanks for your imput on frnash's question! Lake effect snow is the one winter time thing that interests me similarily like supercells do durin the summer!


By frnash on Saturday, December 06, 2008 - 10:10 pm: Edit Post

Thanks to snowfan470 and admin (John) for the explanaton(s).

Now let's see if I can rephrase what you both have said — with my background in engineering and mathematics, and several decades of aviation weather analysis as a pilot — and see if my understanding is somewhere near correct.


1. In the micro environment, with calm wind conditions, the temperature difference between the relatively colder land and the relatively warmer water and thus the corresponding atmospheric pressure differences (higher over the cooler land, lower over the warmer water) would tend to encourage a land breeze (by advection - the horizontal movement of air). The air movement here is at a low level and offshore, ergo no LES!

2. Adding a moderate onshore prevailing wind (apparently both the speed and altitude are critical!?) to this equation causes a collision between these two air masses (a low level convergence), forcing the warmer (less dense) air above the low level land breeze (by convection), thus lifting and transporting the lake-derived moisture — perhaps to a critical altitude for LES generation(?) — as it moves over the land.

3. On the other hand a stronger prevailing onshore wind would tend to inhibit or block the land breeze, (or perhaps force the convergence zone and convection further onshore, over the land?).

4. It seems clear that in addition to the relative temperatures and humidities of these air masses, there are some relatively small scale but extremely critical geometric factors at work here, like the altitude and thickness of the two air masses (the land breeze and the onshore wind) and their points of interaction. (Assuming I'm in the ballpark with the above, this element still remains a bit "fuzzy" to me!)


By sp123 on Saturday, December 06, 2008 - 11:42 pm: Edit Post

yes well however exactly it works i know we can get dumped on. i remember getting about 20 inches of snow a in about 8 hours i think. i pry seen the snow comin down at about inch every 10-15 mins at its heaviest peak. thought only snows that heavy for less than a hour get small breaks in the snow. but we have very easily have gottne 4-5 inches of snow in one hour before from this. john so what if we had light west south west wind for say 15-20 hours straight would we get the snow very heavy for that long of time or would the heavy band move around south to north and north to south. if conditions were favorable


By frnash on Sunday, December 07, 2008 - 10:11 am: Edit Post

"… only snows that heavy for less than a hour get small breaks in the snow."

Yes, I have seen that many times. I can imagine each relatively narrow LES band weaving and flailing back and forth across the area much like the end of an unrestrained garden hose at full pressure.


By admin on Sunday, December 07, 2008 - 11:54 am: Edit Post

That is pretty much it frnash. Only the way I read your explaination (and I may have intrepreted wrong) is that the convergence makes the LES occur, when in fact it only enhances the convection that is already occurring due to the lake/air thermal instability.

sp123-

Such intense bands (4-6"/hr) are typically very narrow (10-30 miles wide) and they do tend to snake around like a flag in the wind, so it is possible to be in and out of such a band. The wider the band, the greater the chance of you staying underneath it for it's duration.

I know one hit where we live now back in December of 2005. It also hit areas of the Trap Rock Valley and I have pics of myself and friends riding in the snow the next day. About 2-3 feet of fluff!

I also know an exceptionally wide bomber hit back in December of 1998. It impacted areas from around Houghton to Phoenix and lasted for over a day. Friends tell me that 3-4 feet was measured in 24 hours from that event.

-John


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