Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260601_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 06/01 18Z 1.19 0204 79 67 3 0.00
Mon 06/01 19Z 0.87 0104 76 60 4 0.01
Mon 06/01 20Z 0.64 0104 76 56 4 0.01
Mon 06/01 21Z 0.29 0003 77 57 4 0.01
Mon 06/01 22Z 0.18 3503 78 57 4 0.01
Mon 06/01 23Z 0.07 3402 79 60 4 0.01
Tue 06/02 00Z 0.09 3303 79 55 4 0.01
Tue 06/02 01Z 0.07 3406 77 52 4 0.00
Tue 06/02 02Z 0.04 3408 74 53 4 0.00
Tue 06/02 03Z 0.05 3509 71 46 4 0.00
Tue 06/02 04Z 0.10 3510 69 41 4 0.00
Tue 06/02 05Z 0.15 3511 68 37 4 0.00
Tue 06/02 06Z 0.13 3510 67 32 4 0.00
Tue 06/02 07Z 0.15 3309 68 33 4 0.00
Tue 06/02 08Z 0.27 3109 69 38 4 0.00
Tue 06/02 09Z 0.36 3011 67 44 4 0.00
Tue 06/02 10Z 0.39 3013 66 46 5 0.00
Tue 06/02 11Z 0.33 3215 63 43 5 0.00
Tue 06/02 12Z 0.24 3216 62 32 5 0.00
Tue 06/02 13Z 0.23 3215 60 24 5 0.00
Tue 06/02 14Z 0.25 3316 55 17 6 0.00
Tue 06/02 15Z 0.29 3317 51 10 6 0.00
Tue 06/02 16Z 1.38 3318 49 5 6 0.00
Tue 06/02 17Z 1.97 3319 47 6 6 0.00
Tue 06/02 18Z 2.45 3320 45 12 6 0.00
Tue 06/02 19Z 2.65 3320 48 21 6 0.00
Tue 06/02 20Z 2.61 3319 52 41 6 0.00
Tue 06/02 21Z 1.84 3319 53 59 7 0.00
Tue 06/02 22Z 0.79 3320 55 75 7 0.00
Tue 06/02 23Z 0.24 3422 55 77 7 0.00
Wed 06/03 00Z 0.14 3423 53 63 7 0.00
Wed 06/03 01Z 0.11 3422 53 44 7 0.00
Wed 06/03 02Z 0.09 3521 52 39 7 0.00
Wed 06/03 03Z 0.17 3519 50 30 7 0.00
Wed 06/03 04Z 0.23 0017 46 25 8 0.00
Wed 06/03 05Z 0.29 0016 43 12 8 0.00
Wed 06/03 06Z 0.22 0014 42 11 8 0.00
Wed 06/03 07Z 0.16 3514 43 11 8 0.00
Wed 06/03 08Z 0.16 3514 43 17 8 0.00
Wed 06/03 09Z 0.15 3513 44 27 8 0.00
Wed 06/03 10Z 0.07 3513 45 38 8 0.00
Wed 06/03 11Z 0.09 3513 44 46 8 0.00
Wed 06/03 12Z 0.06 3511 44 44 8 0.00
Wed 06/03 13Z 0.06 3409 45 60 8 0.00
Wed 06/03 14Z 0.20 3309 47 70 8 0.00
Wed 06/03 15Z 0.32 3209 48 76 9 0.00
Wed 06/03 16Z 0.89 3210 48 76 9 0.00
Wed 06/03 17Z 1.42 3211 47 76 9 0.00
Wed 06/03 18Z 1.48 3210 46 75 10 0.00
Wed 06/03 19Z 1.55 3109 48 70 10 0.00
Wed 06/03 20Z 1.38 3109 50 66 10 0.00
Wed 06/03 21Z 0.83 3110 53 61 11 0.00
Wed 06/03 22Z 0.52 3009 55 57 11 0.00
Wed 06/03 23Z 0.47 2909 57 52 11 0.00
Thu 06/04 00Z 0.46 2809 59 47 11 0.00
Thu 06/04 01Z 0.46 2809 58 40 11 0.00
Thu 06/04 02Z 0.47 2810 59 38 11 0.00
Thu 06/04 03Z 0.42 2910 60 37 11 0.00
Thu 06/04 04Z 0.33 3010 60 34 11 0.00
Thu 06/04 05Z 0.30 3010 58 31 11 0.00
Run total areal avg QPF for the Central_Greens is: 0.06 inches.
Froude Number (Frd#):
Frd# < 0.5 Flow is subcritical and blocked.
Upslope clouds/precip backed farther upwind of and up to mtn crest.
W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
Upslope clouds/precip falls immediately upwind of mtn crest.
W Upslope snow favors western slopes to the Green Mt. spine including:
Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
Gap winds possible.
Frd# 1-2 Flow is critical.
With strong winds, Mountain waves/downslope winds possible.
Precip falls close to mountain ridge crests and on lee side.
W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
Air flows freely over terrain.
Persistent upslope snow not favored. Scattered snow showers and flurries.
Relative Humidity (RH):
925-850 mb RH > 90% needed for upslope precipitation.
with 700mb RH > 70% favors upslope snow.
with 700mb RH > 90% greater amounts of W upslope snow possible.
850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
T > -11 10-15:1
T -11 to -15 25-35:1
T < -15 15-20:1