NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260902_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)
=== ===== === ==== ==== === === === ====
Wed 09/02 06Z 0.03 1712  98  59  12 0.00
Wed 09/02 07Z 0.06 1714  97  60  12 0.01
Wed 09/02 08Z 0.07 1813  95  52  12 0.00
Wed 09/02 09Z 0.07 1812  93  42  11 0.00
Wed 09/02 10Z 0.05 1713  93  37  11 0.00
Wed 09/02 11Z 0.03 1713  92  29  11 0.00
Wed 09/02 12Z 0.03 1614  92  27  11 0.00
Wed 09/02 13Z 0.02 1616  91  29  11 0.00
Wed 09/02 14Z 0.05 1717  92  30  11 0.00
Wed 09/02 15Z 0.08 1816  92  26  12 0.00
Wed 09/02 16Z 0.10 1815  94  26  12 0.00
Wed 09/02 17Z 0.06 1713  94  35  12 0.00
Wed 09/02 18Z 0.05 1715  95  42  12 0.00
Wed 09/02 19Z 0.03 1717  94  46  12 0.00
Wed 09/02 20Z 0.05 1619  92  49  13 0.00
Wed 09/02 21Z 0.03 1721  92  54  13 0.00
Wed 09/02 22Z 0.06 1724  95  70  12 0.00
Wed 09/02 23Z 0.08 1725  95  83  12 0.01
Thu 09/03 00Z 0.06 1726  95  82  13 0.02
Thu 09/03 01Z 0.15 1827  97  83  12 0.01
Thu 09/03 02Z 0.21 1828  98  79  12 0.02
Thu 09/03 03Z 0.26 1928  98  68  12 0.03
Thu 09/03 04Z 0.27 1926  98  76  13 0.05
Thu 09/03 05Z 0.31 1928  98  89  13 0.09
Thu 09/03 06Z 0.32 1930  99  98  13 0.30
Thu 09/03 07Z 0.35 1931  98  95  14 0.46
Thu 09/03 08Z 0.38 2030  99  98  14 0.24
Thu 09/03 09Z 0.43 2128  99  98  14 0.21
Thu 09/03 10Z 0.50 2225  99  96  14 0.19
Thu 09/03 11Z 0.49 2420  99  95  14 0.10
Thu 09/03 12Z 0.43 2616  99  93  14 0.05
Thu 09/03 13Z 0.40 2715  98  97  14 0.03
Thu 09/03 14Z 0.35 2814  93  94  14 0.03
Thu 09/03 15Z 0.32 2913  87  83  14 0.01
Thu 09/03 16Z 0.35 2813  84  67  14 0.00
Thu 09/03 17Z 0.39 2812  81  42  14 0.00
Thu 09/03 18Z 0.46 2812  81  12  14 0.00
Thu 09/03 19Z 0.61 2813  88  11  14 0.01
Thu 09/03 20Z 0.71 2713  91  22  13 0.02
Thu 09/03 21Z 0.76 2715  90  35  13 0.04
Thu 09/03 22Z 0.82 2817  88  27  13 0.01
Thu 09/03 23Z 0.90 2918  86  26  13 0.00
Fri 09/04 00Z 0.84 2918  90  42  12 0.00
Fri 09/04 01Z 0.88 2919  93  43  12 0.01
Fri 09/04 02Z 0.63 3019  93  40  12 0.01
Fri 09/04 03Z 0.53 3019  96  43  11 0.01
Fri 09/04 04Z 0.49 3019  95  26  11 0.01
Fri 09/04 05Z 0.44 3119  96  30  11 0.01
Fri 09/04 06Z 0.34 3119  94  35  11 0.01
Fri 09/04 07Z 0.28 3218  91  23  11 0.00
Fri 09/04 08Z 0.31 3117  92  19  11 0.00
Fri 09/04 09Z 0.29 3117  94  16  11 0.01
Fri 09/04 10Z 0.26 3217  95  14  11 0.01
Fri 09/04 11Z 0.24 3216  93  13  11 0.00
Fri 09/04 12Z 0.26 3217  93  16  10 0.00
Fri 09/04 13Z 0.29 3118  90  16  10 0.00
Fri 09/04 14Z 0.27 3117  86  18  11 0.00
Fri 09/04 15Z 0.27 3116  85  20  11 0.00
Fri 09/04 16Z 0.31 3116  87  20  10 0.00
Fri 09/04 17Z 0.40 3116  90  24  10 0.00

Run total areal avg QPF for the Central_Greens is: 2.02 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