NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260723_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)
=== ===== === ==== ==== === === === ====
Thu 07/23 00Z 0.73 2720  87  28   9 0.00
Thu 07/23 01Z 0.85 2721  89  28   8 0.00
Thu 07/23 02Z 1.00 2824  91  35   7 0.00
Thu 07/23 03Z 1.18 2928  92  39   7 0.01
Thu 07/23 04Z 1.15 3029  91  33   6 0.01
Thu 07/23 05Z 0.94 3028  90  28   5 0.00
Thu 07/23 06Z 0.63 3125  83  27   5 0.00
Thu 07/23 07Z 0.48 3224  76  33   5 0.00
Thu 07/23 08Z 0.52 3224  72  35   5 0.00
Thu 07/23 09Z 0.58 3222  69  33   5 0.00
Thu 07/23 10Z 0.75 3121  69  37   5 0.00
Thu 07/23 11Z 0.76 3020  69  41   6 0.00
Thu 07/23 12Z 0.77 2919  69  38   6 0.00
Thu 07/23 13Z 0.82 2919  66  35   6 0.00
Thu 07/23 14Z 0.98 2917  62  30   6 0.00
Thu 07/23 15Z 2.67 2915  62  28   7 0.00
Thu 07/23 16Z 6.71 2813  66  26   7 0.00
Thu 07/23 17Z 9.12 2713  69  22   7 0.00
Thu 07/23 18Z 9.53 2713  67  22   8 0.00
Thu 07/23 19Z 9.04 2713  67  17   8 0.00
Thu 07/23 20Z 8.64 2713  66  11   9 0.00
Thu 07/23 21Z 6.89 2612  66   9   9 0.00
Thu 07/23 22Z 4.01 2612  66   8   9 0.00
Thu 07/23 23Z 1.96 2712  67   9   9 0.00
Fri 07/24 00Z 1.51 2712  67  10   9 0.00
Fri 07/24 01Z 1.57 2712  69  13   9 0.00
Fri 07/24 02Z 1.12 2711  69  14   9 0.00
Fri 07/24 03Z 0.91 2711  70  15   9 0.00
Fri 07/24 04Z 0.68 2810  68  15   9 0.00
Fri 07/24 05Z 0.57 2810  67  17   9 0.00
Fri 07/24 06Z 0.53 2909  68  18   9 0.00
Fri 07/24 07Z 0.42 2907  67  17   9 0.00
Fri 07/24 08Z 0.33 2906  67  17   9 0.00
Fri 07/24 09Z 0.26 2804  68  17   9 0.00
Fri 07/24 10Z 0.23 2504  68  20   9 0.00
Fri 07/24 11Z 0.19 2304  68  22   9 0.00
Fri 07/24 12Z 0.18 2204  68  22   9 0.00
Fri 07/24 13Z 0.28 2205  70  20   8 0.00
Fri 07/24 14Z 0.63 2206  72  21   8 0.00
Fri 07/24 15Z 1.13 2205  72  21   9 0.00
Fri 07/24 16Z 1.50 2205  71  21   9 0.00
Fri 07/24 17Z 1.83 2406  69  22  10 0.00
Fri 07/24 18Z 1.78 2405  65  25  10 0.00
Fri 07/24 19Z 1.33 2404  62  24  11 0.00
Fri 07/24 20Z 1.12 2504  62  23  11 0.00
Fri 07/24 21Z 0.70 2503  62  23  11 0.00
Fri 07/24 22Z 0.35 2603  61  24  12 0.00
Fri 07/24 23Z 0.20 2602  61  25  12 0.00
Sat 07/25 00Z 0.13 2402  60  25  12 0.00
Sat 07/25 01Z 0.11 2302  61  25  12 0.00
Sat 07/25 02Z 0.08 2201  61  25  12 0.00
Sat 07/25 03Z 0.09 1901  62  26  11 0.00
Sat 07/25 04Z 0.07 1802  62  25  11 0.00
Sat 07/25 05Z 0.06 1703  63  24  11 0.00
Sat 07/25 06Z 0.05 1903  63  24  11 0.00
Sat 07/25 07Z 0.09 2003  63  24  11 0.00
Sat 07/25 08Z 0.03 1901  62  23  11 0.00
Sat 07/25 09Z 0.03 1901  62  22  11 0.00
Sat 07/25 10Z 0.06 1201  62  19  11 0.00
Sat 07/25 11Z 0.12 1203  63  17  11 0.00

Run total areal avg QPF for the greens is: 0.02 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