• Hello, please take a minute to check out our awesome content, contributed by the wonderful members of our community. We hope you'll add your own thoughts and opinions by making a free account!

Pattern Fail or Fab February 2023 Pattern Thread

Myfrotho704_

Tuned 16 veloster turbo, 290 whp/300 whtq
Supporter
Member
Joined
Oct 15, 2018
Messages
30,575
Reaction score
84,387
Location
Concord NC
Yeah, the 6z 3k NAM has midafternoon temps only in the low 70s for RDU. The GFS and European are in the mid 70s. Canadian (as stated above) has mid 80s for RDU.
Nam is always way to cold, it was off by 7 degrees yesterday for example, it’s a known cold bias
 

ILMRoss

Meteorologist
Supporter
Member
Joined
Dec 4, 2018
Messages
327
Reaction score
2,282
Location
Richmond, VA
Nam is always way to cold, it was off by 7 degrees yesterday for example, it’s a known cold bias
a lot of high temp forecasting is simply figuring out how deep boundary layer mixing gets during the day, since mixing will bring those air parcels at 850mb or wherever down adiabatically.

NAM 3km- puts boundary layer at 925mb Thursday afternoon for Richmond. Temp? 75.
nam3km_2023022206_fh36_sounding_KRIC.png

Different model- some WRF model- Boundary layer is around 890mb at same time. Temp? 77.
wrf-arw_2023022200_fh42_sounding_KRIC.png


Nam in my experience underestimates the height of where the boundary layer gets to, whereas the GFS is better or can overestimate sometimes. That's where this nam bias comes from.

But generally that's where a lot of discrepancies will come from, and it's all about just how the model renders turbulence and microphysics and those things are pretty hard to get right. I bet a lot of the NWS forecasts are betting that with how windy it is most models will underestimate the amount of mixing (and don't forget to add some downsloping in their for good measure)

That and cloud cover, but I think ya'll know this, if there's more clouds than forecasted Thursday (totally possible) then the highs will not be all time monthly records. lol.
 

Chazwin

Member
Joined
Dec 12, 2018
Messages
2,964
Reaction score
7,058
Location
Wingate, NC
a lot of high temp forecasting is simply figuring out how deep boundary layer mixing gets during the day, since mixing will bring those air parcels at 850mb or wherever down adiabatically.

NAM 3km- puts boundary layer at 925mb Thursday afternoon for Richmond. Temp? 75.
nam3km_2023022206_fh36_sounding_KRIC.png

Different model- some WRF model- Boundary layer is around 890mb at same time. Temp? 77.
wrf-arw_2023022200_fh42_sounding_KRIC.png


Nam in my experience underestimates the height of where the boundary layer gets to, whereas the GFS is better or can overestimate sometimes. That's where this nam bias comes from.

But generally that's where a lot of discrepancies will come from, and it's all about just how the model renders turbulence and microphysics and those things are pretty hard to get right. I bet a lot of the NWS forecasts are betting that with how windy it is most models will underestimate the amount of mixing (and don't forget to add some downsloping in their for good measure)

That and cloud cover, but I think ya'll know this, if there's more clouds than forecasted Thursday (totally possible) then the highs will not be all time monthly records. lol.
GSP doesn’t seem to be too excited about the idea of setting monthly records tomorrow. They note that the guidance that is pushing highs up over February records also start the day with clear skies… they expect that there will be cloud cover that will take most of the morning to burn off.
 

ILMRoss

Meteorologist
Supporter
Member
Joined
Dec 4, 2018
Messages
327
Reaction score
2,282
Location
Richmond, VA
There's a small difference between the NAM and RDPS.

12z RDPS (midafternoon tomorrow):
View attachment 133488
12z NAM (midafternoon tomorrow):
View attachment 133487
when it's cooler from georgia to VA like this - it's really all about differences in how the model is resolving how deep the boundary layer gets. guarantee you the rdps is a solid 100mb deeper than nam.
 
Top