Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261013_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)
=== ===== === ==== ==== === === === ====
Tue 10/13 06Z 0.07 2902  97  95   7 0.00
Tue 10/13 07Z 0.07 2302  97  98   8 0.00
Tue 10/13 08Z 0.04 1704  98  99   7 0.02
Tue 10/13 09Z 0.07 1611  98  99   8 0.05
Tue 10/13 10Z 0.11 1619  98  99   7 0.07
Tue 10/13 11Z 0.07 1623  98  95   7 0.09
Tue 10/13 12Z 0.05 1724  97  94   9 0.11
Tue 10/13 13Z 0.08 1725  97  98   9 0.11
Tue 10/13 14Z 0.11 1826  97  82  10 0.10
Tue 10/13 15Z 0.09 1729  98  73  10 0.04
Tue 10/13 16Z 0.10 1831  97  65  10 0.04
Tue 10/13 17Z 0.12 1833  98  83  11 0.04
Tue 10/13 18Z 0.13 1835  98  94  11 0.11
Tue 10/13 19Z 0.21 1933  98  98  11 0.21
Tue 10/13 20Z 0.28 2030  98  98  12 0.16
Tue 10/13 21Z 0.35 2129  98  96  12 0.08
Tue 10/13 22Z 0.42 2228  99  89  12 0.17
Tue 10/13 23Z 0.45 2226  99  83  13 0.10
Wed 10/14 00Z 0.49 2327  99  82  13 0.05
Wed 10/14 01Z 0.55 2328  99  80  14 0.04
Wed 10/14 02Z 0.59 2427  97  78  14 0.04
Wed 10/14 03Z 0.62 2427  97  76  14 0.03
Wed 10/14 04Z 0.64 2427  97  79  14 0.04
Wed 10/14 05Z 0.66 2426  96  74  14 0.09
Wed 10/14 06Z 0.78 2529  97  77  13 0.04
Wed 10/14 07Z 0.90 2530  98  60  13 0.03
Wed 10/14 08Z 1.01 2532  97  27  12 0.03
Wed 10/14 09Z 1.19 2633  97  20  11 0.03
Wed 10/14 10Z 1.25 2732  97  15  10 0.03
Wed 10/14 11Z 0.95 2731  96  11   9 0.02
Wed 10/14 12Z 0.71 2831  94   9  10 0.01
Wed 10/14 13Z 0.62 2831  92  16  10 0.01
Wed 10/14 14Z 0.57 2831  91  15   9 0.01
Wed 10/14 15Z 0.55 2829  91  20   9 0.01
Wed 10/14 16Z 0.50 2827  89  37   9 0.00
Wed 10/14 17Z 0.53 2827  90  61   8 0.01
Wed 10/14 18Z 0.54 2926  92  71   7 0.01
Wed 10/14 19Z 0.52 2926  91  78   7 0.01
Wed 10/14 20Z 0.50 2925  93  76   6 0.01
Wed 10/14 21Z 0.46 3024  93  75   5 0.01
Wed 10/14 22Z 0.40 3023  94  72   5 0.00
Wed 10/14 23Z 0.41 3023  95  62   4 0.01
Thu 10/15 00Z 0.38 3124  94  52   4 0.01
Thu 10/15 01Z 0.38 3126  93  25   3 0.01
Thu 10/15 02Z 0.36 3126  91  24   3 0.01
Thu 10/15 03Z 0.38 3128  92  24   3 0.00
Thu 10/15 04Z 0.41 3230  92  20   2 0.00
Thu 10/15 05Z 0.35 3229  89   7   1 0.00
Thu 10/15 06Z 0.33 3230  82   4   1 0.00
Thu 10/15 07Z 0.29 3231  82   4   1 0.01
Thu 10/15 08Z 0.26 3331  79   2   0 0.01
Thu 10/15 09Z 0.22 3331  77   4   0 0.01
Thu 10/15 10Z 0.15 3329  78   3   0 0.01
Thu 10/15 11Z 0.11 3427  80   3   0 0.01
Thu 10/15 12Z 0.09 3426  81   2   0 0.01
Thu 10/15 13Z 0.06 3423  80   2   0 0.01
Thu 10/15 14Z 0.04 3420  80   3   0 0.00
Thu 10/15 15Z 0.03 3417  78   3   0 0.00
Thu 10/15 16Z 0.01 3416  71   4   0 0.00
Thu 10/15 17Z 0.02 3413  63   5   1 0.00

Run total areal avg QPF for the Central_Greens is: 2.17 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