NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260905_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)
=== ===== === ==== ==== === === === ====
Sat 09/05 06Z 0.13 3412  93  84  10 0.00
Sat 09/05 07Z 0.15 3313  90  83  10 0.00
Sat 09/05 08Z 0.12 3414  89  82  10 0.01
Sat 09/05 09Z 0.08 3414  88  81  10 0.01
Sat 09/05 10Z 0.05 3515  87  83  10 0.01
Sat 09/05 11Z 0.05 0016  88  82   9 0.01
Sat 09/05 12Z 0.08 0016  90  79   9 0.00
Sat 09/05 13Z 0.11 0116  93  77   9 0.00
Sat 09/05 14Z 0.14 0113  96  78   8 0.00
Sat 09/05 15Z 0.14 0111  96  75   8 0.00
Sat 09/05 16Z 0.11 0110  97  74   8 0.00
Sat 09/05 17Z 0.09 0109  96  73   8 0.00
Sat 09/05 18Z 0.12 0109  97  72   9 0.01
Sat 09/05 19Z 0.10 0109  97  73   9 0.01
Sat 09/05 20Z 0.14 0108  97  78   9 0.03
Sat 09/05 21Z 0.17 0208  95  83   9 0.04
Sat 09/05 22Z 0.24 0309  93  86   9 0.04
Sat 09/05 23Z 0.28 0410  94  93   9 0.04
Sun 09/06 00Z 0.36 0512  95  94   9 0.03
Sun 09/06 01Z 0.44 0612  95  95   8 0.03
Sun 09/06 02Z 0.56 0813  94  96   8 0.05
Sun 09/06 03Z 0.56 0813  92  96   7 0.03
Sun 09/06 04Z 0.51 0812  89  96   7 0.02
Sun 09/06 05Z 0.48 0812  85  96   7 0.02
Sun 09/06 06Z 0.44 0811  88  98   6 0.04
Sun 09/06 07Z 0.39 0710  90  98   6 0.04
Sun 09/06 08Z 0.30 0509  88  96   6 0.03
Sun 09/06 09Z 0.22 0309  84  93   6 0.02
Sun 09/06 10Z 0.15 0210  82  88   6 0.01
Sun 09/06 11Z 0.13 0110  79  83   6 0.00
Sun 09/06 12Z 0.11 0112  78  74   6 0.00
Sun 09/06 13Z 0.09 0112  78  66   6 0.00
Sun 09/06 14Z 0.13 0114  78  55   6 0.00
Sun 09/06 15Z 0.19 0114  76  45   6 0.00
Sun 09/06 16Z 0.21 0012  77  41   6 0.00
Sun 09/06 17Z 0.22 0012  78  39   6 0.00
Sun 09/06 18Z 0.34 3512  81  39   6 0.00
Sun 09/06 19Z 0.73 3412  85  26   6 0.00
Sun 09/06 20Z 0.77 3414  87  22   6 0.00
Sun 09/06 21Z 0.53 3415  88  15   6 0.00
Sun 09/06 22Z 0.33 3416  87  12   6 0.00
Sun 09/06 23Z 0.30 3419  89  15   6 0.01
Mon 09/07 00Z 0.19 3421  85   9   6 0.01
Mon 09/07 01Z 0.18 3422  85  11   7 0.01
Mon 09/07 02Z 0.18 3422  89   9   6 0.01
Mon 09/07 03Z 0.14 3523  90  11   6 0.01
Mon 09/07 04Z 0.09 3522  89  11   6 0.01
Mon 09/07 05Z 0.04 3521  87   7   6 0.00
Mon 09/07 06Z 0.04 3521  83   4   6 0.00
Mon 09/07 07Z 0.04 3521  82   5   6 0.00
Mon 09/07 08Z 0.09 3520  80   6   6 0.00
Mon 09/07 09Z 0.09 3520  77   6   6 0.00
Mon 09/07 10Z 0.11 3519  75   7   6 0.00
Mon 09/07 11Z 0.15 3419  76   7   6 0.00
Mon 09/07 12Z 0.23 3419  80   7   5 0.00
Mon 09/07 13Z 0.28 3418  82   7   5 0.00
Mon 09/07 14Z 0.29 3318  82   7   5 0.00
Mon 09/07 15Z 0.33 3318  81   6   5 0.00
Mon 09/07 16Z 0.43 3318  82   5   6 0.00
Mon 09/07 17Z 1.09 3316  84   5   6 0.00

Run total areal avg QPF for the greens is: 0.59 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