NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260722_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)
=== ===== === ==== ==== === === === ====
Wed 07/22 06Z 0.26 2019  97  87  14 0.00
Wed 07/22 07Z 0.25 2022  98  92  14 0.02
Wed 07/22 08Z 0.44 2124  98  86  14 0.16
Wed 07/22 09Z 0.72 2325  99  82  14 0.19
Wed 07/22 10Z 0.69 2520  97  68  14 0.08
Wed 07/22 11Z 0.55 2615  97  65  13 0.01
Wed 07/22 12Z 0.52 2514  97  80  13 0.01
Wed 07/22 13Z 0.53 2514  95  87  13 0.01
Wed 07/22 14Z 0.62 2516  96  95  13 0.06
Wed 07/22 15Z 0.61 2517  88  89  13 0.03
Wed 07/22 16Z 1.48 2420  90  74  12 0.00
Wed 07/22 17Z 1.90 2422  94  51  12 0.06
Wed 07/22 18Z 1.11 2525  90  31  11 0.07
Wed 07/22 19Z 2.32 2525  91  36  11 0.02
Wed 07/22 20Z 4.13 2524  89  48  10 0.01
Wed 07/22 21Z 5.62 2524  87  51   9 0.01
Wed 07/22 22Z 5.59 2625  86  47   9 0.00
Wed 07/22 23Z 1.87 2625  89  43   8 0.00
Thu 07/23 00Z 1.59 2725  91  38   8 0.00
Thu 07/23 01Z 1.26 2725  94  33   7 0.01
Thu 07/23 02Z 1.18 2825  94  32   6 0.01
Thu 07/23 03Z 0.99 2924  94  34   6 0.00
Thu 07/23 04Z 0.87 2924  94  31   5 0.00
Thu 07/23 05Z 0.70 3025  90  28   6 0.00
Thu 07/23 06Z 0.62 3126  85  28   6 0.00
Thu 07/23 07Z 0.55 3125  81  33   6 0.00
Thu 07/23 08Z 0.47 3224  72  41   6 0.00
Thu 07/23 09Z 0.39 3222  61  40   6 0.00
Thu 07/23 10Z 0.36 3220  56  35   6 0.00
Thu 07/23 11Z 0.40 3117  54  29   6 0.00
Thu 07/23 12Z 0.50 3016  57  23   6 0.00
Thu 07/23 13Z 0.71 2916  68  18   6 0.00
Thu 07/23 14Z 1.15 2817  74  21   6 0.00
Thu 07/23 15Z 2.50 2716  72  28   6 0.00
Thu 07/23 16Z 5.66 2615  77  28   6 0.00
Thu 07/23 17Z 7.51 2614  80  22   7 0.00
Thu 07/23 18Z 6.95 2614  79  21   7 0.00
Thu 07/23 19Z 5.72 2613  78  17   8 0.00
Thu 07/23 20Z 4.66 2611  77  14   8 0.00
Thu 07/23 21Z 3.65 2611  77  21   9 0.00
Thu 07/23 22Z 2.05 2511  77  25   9 0.00
Thu 07/23 23Z 1.12 2511  77  28   9 0.00
Fri 07/24 00Z 0.85 2511  75  24   9 0.00
Fri 07/24 01Z 0.75 2511  74  21   9 0.00
Fri 07/24 02Z 0.78 2511  73  17   9 0.00
Fri 07/24 03Z 0.80 2511  74  14   9 0.00
Fri 07/24 04Z 0.66 2510  72  12   9 0.00
Fri 07/24 05Z 0.52 2510  70  13   9 0.00
Fri 07/24 06Z 0.43 2510  66  16   9 0.00
Fri 07/24 07Z 0.44 2510  65  16   9 0.00
Fri 07/24 08Z 0.42 2509  65  16   9 0.00
Fri 07/24 09Z 0.39 2508  63  17   9 0.00
Fri 07/24 10Z 0.30 2407  60  18   9 0.00
Fri 07/24 11Z 0.26 2306  57  19   9 0.00
Fri 07/24 12Z 0.24 2306  54  21   9 0.00
Fri 07/24 13Z 0.23 2406  51  21   9 0.00
Fri 07/24 14Z 0.21 2304  49  19  10 0.00
Fri 07/24 15Z 0.43 2304  52  17  10 0.00
Fri 07/24 16Z 0.51 2203  52  16  10 0.00
Fri 07/24 17Z 0.58 2103  51  16  10 0.00

Run total areal avg QPF for the greens is: 0.76 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