NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260723_0600
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 06Z 0.74 3125  90  41   6 0.00
Thu 07/23 07Z 0.69 3125  82  37   6 0.00
Thu 07/23 08Z 0.61 3124  79  39   6 0.00
Thu 07/23 09Z 0.57 3125  75  51   6 0.00
Thu 07/23 10Z 0.55 3124  73  50   6 0.00
Thu 07/23 11Z 0.51 3121  73  36   6 0.00
Thu 07/23 12Z 0.43 3017  70  25   7 0.00
Thu 07/23 13Z 0.44 3015  69  34   7 0.00
Thu 07/23 14Z 0.50 2914  68  40   7 0.00
Thu 07/23 15Z 0.64 2813  67  44   7 0.00
Thu 07/23 16Z 1.23 2713  67  49   7 0.00
Thu 07/23 17Z 2.88 2614  71  56   8 0.00
Thu 07/23 18Z 7.07 2615  74  49   8 0.00
Thu 07/23 19Z 10.59 2716  69  38   9 0.00
Thu 07/23 20Z 8.65 2716  66  31   9 0.00
Thu 07/23 21Z 8.17 2715  65  24   9 0.00
Thu 07/23 22Z 4.94 2714  63  22   9 0.00
Thu 07/23 23Z 1.88 2716  65  34   9 0.00
Fri 07/24 00Z 1.99 2717  63  35  10 0.00
Fri 07/24 01Z 1.45 2716  62  27  10 0.00
Fri 07/24 02Z 1.12 2715  61  25  10 0.00
Fri 07/24 03Z 1.06 2716  59  23  10 0.00
Fri 07/24 04Z 0.95 2715  59  25   9 0.00
Fri 07/24 05Z 0.84 2815  58  26  10 0.00
Fri 07/24 06Z 0.77 2814  58  25  10 0.00
Fri 07/24 07Z 0.73 2813  59  22  10 0.00
Fri 07/24 08Z 0.70 2812  61  23   9 0.00
Fri 07/24 09Z 0.71 2911  64  25   9 0.00
Fri 07/24 10Z 0.59 2910  66  23   9 0.00
Fri 07/24 11Z 0.50 2808  65  20   9 0.00
Fri 07/24 12Z 0.50 2808  61  22   9 0.00
Fri 07/24 13Z 0.42 2707  62  25   9 0.00
Fri 07/24 14Z 0.50 2505  63  26   9 0.00
Fri 07/24 15Z 0.75 2305  63  26  10 0.00
Fri 07/24 16Z 1.03 2205  62  27  10 0.00
Fri 07/24 17Z 1.61 2205  61  26  10 0.00
Fri 07/24 18Z 1.43 2204  59  26  11 0.00
Fri 07/24 19Z 1.04 2303  57  26  11 0.00
Fri 07/24 20Z 0.49 2102  56  26  12 0.00
Fri 07/24 21Z 0.32 2102  57  25  12 0.00
Fri 07/24 22Z 0.21 1802  58  23  12 0.00
Fri 07/24 23Z 0.14 1603  60  22  12 0.00
Sat 07/25 00Z 0.09 1705  60  23  12 0.00
Sat 07/25 01Z 0.09 1706  61  23  12 0.00
Sat 07/25 02Z 0.08 1806  61  23  12 0.00
Sat 07/25 03Z 0.08 1807  60  24  12 0.00
Sat 07/25 04Z 0.06 1707  61  24  12 0.00
Sat 07/25 05Z 0.05 1808  61  24  11 0.00
Sat 07/25 06Z 0.04 1806  60  24  11 0.00
Sat 07/25 07Z 0.04 1805  59  23  12 0.00
Sat 07/25 08Z 0.07 1605  58  22  12 0.00
Sat 07/25 09Z 0.14 1406  56  21  12 0.00
Sat 07/25 10Z 0.18 1408  54  20  12 0.00
Sat 07/25 11Z 0.17 1508  57  19  11 0.00
Sat 07/25 12Z 0.21 1509  61  18  11 0.00
Sat 07/25 13Z 0.22 1510  66  17  11 0.00
Sat 07/25 14Z 0.43 1510  68  16  10 0.00
Sat 07/25 15Z 0.66 1509  66  15  11 0.00
Sat 07/25 16Z 0.76 1408  63  13  11 0.00
Sat 07/25 17Z 1.24 1308  61  11  11 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