Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261022_1800
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)
=== ===== === ==== ==== === === === ====
Thu 10/22 18Z 0.16 3416  74  55   3 0.00
Thu 10/22 19Z 0.24 3421  79  56   3 0.00
Thu 10/22 20Z 0.10 3427  83  42   3 0.00
Thu 10/22 21Z 0.06 3429  83  27   2 0.00
Thu 10/22 22Z 0.08 3530  74  21   3 0.00
Thu 10/22 23Z 0.18 0032  75  17   2 0.00
Fri 10/23 00Z 0.26 0032  79  19   1 0.00
Fri 10/23 01Z 0.28 0031  71  17   1 0.00
Fri 10/23 02Z 0.28 0129  61  14   1 0.00
Fri 10/23 03Z 0.29 0127  60  11   1 0.00
Fri 10/23 04Z 0.32 0126  63   4   1 0.00
Fri 10/23 05Z 0.38 0226  55   1   0 0.00
Fri 10/23 06Z 0.39 0225  47   1   0 0.00
Fri 10/23 07Z 0.37 0224  44   1   0 0.00
Fri 10/23 08Z 0.34 0223  41   2   0 0.00
Fri 10/23 09Z 0.31 0223  41   2   0 0.00
Fri 10/23 10Z 0.31 0225  40   1   0 0.00
Fri 10/23 11Z 0.34 0225  38   1   0 0.00
Fri 10/23 12Z 0.35 0225  32   1   0 0.00
Fri 10/23 13Z 0.33 0224  29   1   0 0.00
Fri 10/23 14Z 0.29 0221  31   3   0 0.00
Fri 10/23 15Z 0.25 0219  36   4   0 0.00
Fri 10/23 16Z 0.24 0216  38   3   0 0.00
Fri 10/23 17Z 0.22 0215  39   3   0 0.00
Fri 10/23 18Z 0.20 0213  40   2   1 0.00
Fri 10/23 19Z 0.17 0212  37   1   2 0.00
Fri 10/23 20Z 0.15 0212  34   1   3 0.00
Fri 10/23 21Z 0.14 0212  31   2   3 0.00
Fri 10/23 22Z 0.15 0213  25   2   4 0.00
Fri 10/23 23Z 0.15 0212  22   2   4 0.00
Sat 10/24 00Z 0.14 0211  19   3   5 0.00
Sat 10/24 01Z 0.12 0210  17   3   5 0.00
Sat 10/24 02Z 0.10 0208  14   3   5 0.00
Sat 10/24 03Z 0.07 0207  12   2   5 0.00
Sat 10/24 04Z 0.05 0105  10   2   5 0.00
Sat 10/24 05Z 0.03 0104  10   2   5 0.00
Sat 10/24 06Z 0.01 3504   9   1   5 0.00
Sat 10/24 07Z 0.04 3204   8   1   5 0.00
Sat 10/24 08Z 0.08 3106   8   1   5 0.00
Sat 10/24 09Z 0.10 3108   8   2   5 0.00
Sat 10/24 10Z 0.11 3210   8   2   5 0.00
Sat 10/24 11Z 0.10 3212   7   2   4 0.00
Sat 10/24 12Z 0.08 3312   8   2   4 0.00
Sat 10/24 13Z 0.06 3311   8   1   5 0.00
Sat 10/24 14Z 0.05 3310   8   1   5 0.00
Sat 10/24 15Z 0.05 3309   9   1   5 0.00
Sat 10/24 16Z 0.06 3309  12   1   5 0.00
Sat 10/24 17Z 0.07 3208  14   1   5 0.00
Sat 10/24 18Z 0.08 3208  16   2   5 0.00
Sat 10/24 19Z 0.09 3209  16   3   5 0.00
Sat 10/24 20Z 0.08 3310  15   5   5 0.00
Sat 10/24 21Z 0.06 3311  12  13   5 0.00
Sat 10/24 22Z 0.03 3410   9  23   5 0.00
Sat 10/24 23Z 0.02 3409   8  33   6 0.00
Sun 10/25 00Z 0.02 3409   8  47   6 0.00
Sun 10/25 01Z 0.02 3408   8  56   6 0.00
Sun 10/25 02Z 0.02 3406   9  56   6 0.00
Sun 10/25 03Z 0.04 3305   9  56   6 0.00
Sun 10/25 04Z 0.05 3104   8  56   6 0.00
Sun 10/25 05Z 0.07 3004   8  59   7 0.00

Run total areal avg QPF for the Central_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