Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261028_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 10/28 00Z 0.20 3111  55   7   0 0.00
Wed 10/28 01Z 0.19 3110  54   6   0 0.00
Wed 10/28 02Z 0.16 3211  53   6   0 0.00
Wed 10/28 03Z 0.12 3209  51   5   0 0.00
Wed 10/28 04Z 0.08 3307  47   5   0 0.00
Wed 10/28 05Z 0.07 3205  44   4   1 0.00
Wed 10/28 06Z 0.05 3002  40   5   1 0.00
Wed 10/28 07Z 0.06 2502  37   5   2 0.00
Wed 10/28 08Z 0.10 2305  35   7   2 0.00
Wed 10/28 09Z 0.15 2407  36  16   2 0.00
Wed 10/28 10Z 0.17 2408  35  36   2 0.00
Wed 10/28 11Z 0.18 2409  35  55   2 0.00
Wed 10/28 12Z 0.18 2509  33  71   3 0.00
Wed 10/28 13Z 0.19 2509  32  68   3 0.00
Wed 10/28 14Z 0.22 2411  33  71   3 0.00
Wed 10/28 15Z 0.24 2512  31  76   4 0.00
Wed 10/28 16Z 0.23 2511  29  73   4 0.00
Wed 10/28 17Z 0.23 2511  29  77   5 0.00
Wed 10/28 18Z 0.23 2511  27  79   5 0.00
Wed 10/28 19Z 0.23 2511  26  84   6 0.00
Wed 10/28 20Z 0.25 2611  28  90   6 0.00
Wed 10/28 21Z 0.27 2612  31  90   7 0.00
Wed 10/28 22Z 0.28 2613  37  81   7 0.00
Wed 10/28 23Z 0.29 2613  40  81   8 0.00
Thu 10/29 00Z 0.32 2514  44  76   8 0.00
Thu 10/29 01Z 0.32 2514  50  70   8 0.00
Thu 10/29 02Z 0.33 2514  56  57   8 0.00
Thu 10/29 03Z 0.35 2415  65  54   8 0.00
Thu 10/29 04Z 0.36 2415  71  48   8 0.00
Thu 10/29 05Z 0.37 2416  75  41   8 0.00
Thu 10/29 06Z 0.39 2418  77  30   8 0.00
Thu 10/29 07Z 0.42 2419  78  24   8 0.00
Thu 10/29 08Z 0.46 2420  79  25   7 0.01
Thu 10/29 09Z 0.49 2420  82  26   7 0.01
Thu 10/29 10Z 0.52 2520  91  21   7 0.01
Thu 10/29 11Z 0.54 2620  94  18   6 0.01
Thu 10/29 12Z 0.56 2620  94  16   6 0.01
Thu 10/29 13Z 0.59 2621  94   9   6 0.01
Thu 10/29 14Z 0.63 2522  94  11   6 0.01
Thu 10/29 15Z 0.69 2524  92  24   6 0.00
Thu 10/29 16Z 0.67 2424  88  32   6 0.00
Thu 10/29 17Z 0.69 2424  89  31   6 0.00
Thu 10/29 18Z 0.69 2424  87  49   7 0.00
Thu 10/29 19Z 0.66 2424  83  39   8 0.00
Thu 10/29 20Z 0.75 2526  86  47   8 0.00
Thu 10/29 21Z 0.78 2529  86  37   8 0.00
Thu 10/29 22Z 0.77 2531  84  49   9 0.00
Thu 10/29 23Z 0.78 2532  82  63   9 0.01
Fri 10/30 00Z 0.86 2534  86  81   9 0.01
Fri 10/30 01Z 0.99 2535  91  87   8 0.01
Fri 10/30 02Z 1.04 2536  91  89   8 0.01
Fri 10/30 03Z 1.07 2636  93  81   7 0.03
Fri 10/30 04Z 1.07 2633  96  62   7 0.02
Fri 10/30 05Z 1.00 2731  96  36   7 0.03
Fri 10/30 06Z 0.89 2829  90  21   6 0.02
Fri 10/30 07Z 0.84 2827  86  13   6 0.02
Fri 10/30 08Z 0.77 2826  81   8   5 0.02
Fri 10/30 09Z 0.73 2825  81   8   5 0.01
Fri 10/30 10Z 0.76 2825  82   6   4 0.01
Fri 10/30 11Z 0.76 2826  83   7   4 0.02

Run total areal avg QPF for the greens is: 0.29 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