NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20251015_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 10/15 00Z 0.13 3313  86  73   9 0.00
Wed 10/15 03Z 0.21 3319  85  58   7 0.00
Wed 10/15 06Z 0.32 3319  85  23   6 0.00
Wed 10/15 09Z 0.18 3418  86  13   4 0.00
Wed 10/15 12Z 0.18 3318  89  11   1 0.00
Wed 10/15 15Z 0.31 3321  77  15   0 0.00
Wed 10/15 18Z 0.45 3422  72  17  -2 0.00
Wed 10/15 21Z 1.66 3422  79  21  -3 0.00
Thu 10/16 00Z 0.61 3424  86   8  -4 0.00
Thu 10/16 03Z 0.34 3426  89   9  -5 0.00
Thu 10/16 06Z 0.21 3525  91   7  -6 0.00
Thu 10/16 09Z 0.29 3525  91  15  -6 0.00
Thu 10/16 12Z 0.28 3526  91  24  -6 0.00
Thu 10/16 15Z 0.38 3422  90  29  -6 0.00
Thu 10/16 18Z 1.31 3421  85  57  -4 0.00
Thu 10/16 21Z 1.74 3424  83  73  -4 0.00
Fri 10/17 00Z 0.07 3528  77  80  -2 0.00
Fri 10/17 03Z 0.16 0126  78  75   0 0.00
Fri 10/17 06Z 0.20 0124  85  66   0 0.00
Fri 10/17 09Z 0.13 0119  85  52   0 0.00
Fri 10/17 12Z 0.10 0120  79  37   2 0.00
Fri 10/17 15Z 0.04 3515  80  22   1 0.00
Fri 10/17 18Z 0.13 3413  72   8   1 0.00
Fri 10/17 21Z 0.02 3516  77  22   1 0.00
Sat 10/18 00Z 0.10 3420  49   8   3 0.00
Sat 10/18 03Z 0.03 3516  49  41   3 0.00
Sat 10/18 06Z 0.07 3414  48  65   4 0.00
Sat 10/18 09Z 0.06 3412  37  72   4 0.00
Sat 10/18 12Z 0.06 3411  30  72   6 0.00

Run total areal avg QPF for the greens is: 0.00 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