NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260722_0600
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)
=== ===== === ==== ==== === === === ====
Wed 07/22 06Z 0.38 2119  98  87  14 0.00
Wed 07/22 07Z 0.36 2021  99  93  14 0.03
Wed 07/22 08Z 0.62 2126  98  81  14 0.10
Wed 07/22 09Z 0.84 2426  99  77  14 0.04
Wed 07/22 10Z 0.70 2520  97  67  14 0.04
Wed 07/22 11Z 0.54 2615  97  65  14 0.01
Wed 07/22 12Z 0.53 2514  96  75  13 0.01
Wed 07/22 13Z 0.56 2514  96  84  13 0.01
Wed 07/22 14Z 0.65 2516  97  94  13 0.06
Wed 07/22 15Z 0.66 2518  90  90  13 0.04
Wed 07/22 16Z 1.06 2520  89  73  13 0.00
Wed 07/22 17Z 2.60 2424  93  54  12 0.06
Wed 07/22 18Z 1.27 2524  91  18  12 0.04
Wed 07/22 19Z 3.04 2525  89  28  11 0.02
Wed 07/22 20Z 5.48 2524  88  44  10 0.01
Wed 07/22 21Z 6.79 2624  86  45  10 0.00
Wed 07/22 22Z 7.39 2625  84  43   9 0.00
Wed 07/22 23Z 1.93 2624  87  38   9 0.00
Thu 07/23 00Z 1.64 2724  89  30   8 0.00
Thu 07/23 01Z 1.17 2724  92  26   7 0.00
Thu 07/23 02Z 1.02 2823  94  26   7 0.01
Thu 07/23 03Z 0.80 2923  94  26   6 0.00
Thu 07/23 04Z 0.67 2922  93  23   6 0.00
Thu 07/23 05Z 0.50 3124  88  22   6 0.00
Thu 07/23 06Z 0.41 3125  84  22   6 0.00
Thu 07/23 07Z 0.32 3224  80  27   6 0.00
Thu 07/23 08Z 0.28 3222  73  39   6 0.00
Thu 07/23 09Z 0.23 3221  63  40   6 0.00
Thu 07/23 10Z 0.20 3320  54  31   7 0.00
Thu 07/23 11Z 0.24 3217  52  23   6 0.00
Thu 07/23 12Z 0.35 3115  58  21   6 0.00
Thu 07/23 13Z 0.51 3015  68  16   6 0.00
Thu 07/23 14Z 0.99 2915  73  18   6 0.00
Thu 07/23 15Z 2.40 2714  74  22   6 0.00
Thu 07/23 16Z 4.47 2713  78  22   7 0.00
Thu 07/23 17Z 5.61 2613  82  22   7 0.00
Thu 07/23 18Z 5.25 2613  82  18   7 0.00
Thu 07/23 19Z 3.82 2512  82  18   8 0.00
Thu 07/23 20Z 2.90 2511  81  16   8 0.00
Thu 07/23 21Z 1.97 2510  80  18   9 0.00
Thu 07/23 22Z 1.05 2510  81  22   9 0.00
Thu 07/23 23Z 0.79 2510  82  25   9 0.00
Fri 07/24 00Z 0.64 2510  78  20   9 0.00
Fri 07/24 01Z 0.63 2510  76  16   9 0.00
Fri 07/24 02Z 0.56 2510  73  13   9 0.00
Fri 07/24 03Z 0.55 2510  75  10   9 0.00
Fri 07/24 04Z 0.48 2509  72   9  10 0.00
Fri 07/24 05Z 0.43 2509  69  10  10 0.00
Fri 07/24 06Z 0.36 2508  67  13  10 0.00
Fri 07/24 07Z 0.35 2408  67  15  10 0.00
Fri 07/24 08Z 0.32 2408  67  15   9 0.00
Fri 07/24 09Z 0.29 2407  64  16   9 0.00
Fri 07/24 10Z 0.21 2305  61  15   9 0.00
Fri 07/24 11Z 0.17 2205  56  17  10 0.00
Fri 07/24 12Z 0.17 2305  51  18  10 0.00
Fri 07/24 13Z 0.16 2404  46  18  10 0.00
Fri 07/24 14Z 0.12 2303  43  15  10 0.00
Fri 07/24 15Z 0.24 2203  46  14  10 0.00
Fri 07/24 16Z 0.33 2103  46  14  10 0.00
Fri 07/24 17Z 0.51 2103  46  14  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.48 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