NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20250319_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 03/19 00Z 0.23 2111  35  23   3 0.00
Wed 03/19 03Z 0.46 2416  28  40   4 0.00
Wed 03/19 06Z 0.45 2514  32  42   5 0.00
Wed 03/19 09Z 0.29 2510  35  35   6 0.00
Wed 03/19 12Z 0.25 2211  33  36   6 0.00
Wed 03/19 15Z 0.21 2019  30  34   8 0.00
Wed 03/19 18Z 0.22 2024  32  27   9 0.00
Wed 03/19 21Z 0.20 1925  36  19   9 0.00
Thu 03/20 00Z 0.19 1934  33   9  10 0.00
Thu 03/20 03Z 0.23 1940  28   6  11 0.00
Thu 03/20 06Z 0.24 1941  30   8  10 0.00
Thu 03/20 09Z 0.27 1941  30   7  10 0.00
Thu 03/20 12Z 0.26 1944  38   5   9 0.00
Thu 03/20 15Z 0.24 1944  56   7   9 0.00
Thu 03/20 18Z 0.19 1940  68   8   9 0.00
Thu 03/20 21Z 0.16 1940  71  16   8 0.00
Fri 03/21 00Z 0.20 1940  79  24   6 0.00
Fri 03/21 03Z 0.41 2125  97  97   3 0.01
Fri 03/21 06Z 0.86 2617  97  87   0 0.05
Fri 03/21 09Z 0.61 3021  94  57  -4 0.02
Fri 03/21 12Z 0.37 3227  93  40  -7 0.01
Fri 03/21 15Z 0.28 3327  76   5  -8 0.00
Fri 03/21 18Z 2.84 3324  44   3  -9 0.00
Fri 03/21 21Z 0.37 3326  71  16  -8 0.00
Sat 03/22 00Z 0.24 3323  39  37  -5 0.00
Sat 03/22 03Z 0.19 3318  33  36  -3 0.00
Sat 03/22 06Z 0.18 3110  30  57  -2 0.00
Sat 03/22 09Z 0.26 2610  34  41  -2 0.00
Sat 03/22 12Z 0.25 2114  29  36  -2 0.00

Run total areal avg QPF for the greens is: 0.09 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