NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260415_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)
=== ===== === ==== ==== === === === ====
Wed 04/15 18Z 0.30 2013  83  94  11 0.00
Wed 04/15 19Z 0.65 2217  85  95  11 0.00
Wed 04/15 20Z 1.37 2320  86  85  12 0.00
Wed 04/15 21Z 0.94 2519  83  75  12 0.00
Wed 04/15 22Z 0.71 2615  84  69  12 0.00
Wed 04/15 23Z 0.76 2615  93  84  11 0.00
Thu 04/16 00Z 0.75 2617  94  82  11 0.01
Thu 04/16 01Z 0.69 2617  93  89  11 0.00
Thu 04/16 02Z 0.47 2714  87  87  11 0.00
Thu 04/16 03Z 0.40 2613  86  90  12 0.00
Thu 04/16 04Z 0.38 2512  86  94  12 0.00
Thu 04/16 05Z 0.44 2613  89  95  11 0.02
Thu 04/16 06Z 0.43 2613  93  94  11 0.17
Thu 04/16 07Z 0.30 2610  89  95  11 0.07
Thu 04/16 08Z 0.23 2408  89  96  11 0.05
Thu 04/16 09Z 0.26 2509  91  98  11 0.03
Thu 04/16 10Z 0.21 2407  90  93  11 0.02
Thu 04/16 11Z 0.23 2408  91  93  11 0.01
Thu 04/16 12Z 0.21 2308  92  83  11 0.01
Thu 04/16 13Z 0.27 2709  94  83  11 0.01
Thu 04/16 14Z 0.23 2707  94  75  11 0.00
Thu 04/16 15Z 0.22 2607  93  55  11 0.00
Thu 04/16 16Z 0.27 2608  92  53  11 0.00
Thu 04/16 17Z 0.29 2509  87  66  12 0.00
Thu 04/16 18Z 0.34 2510  86  69  12 0.00
Thu 04/16 19Z 0.37 2310  87  73  12 0.00
Thu 04/16 20Z 0.41 2211  83  60  12 0.00
Thu 04/16 21Z 0.36 2111  80  40  13 0.00
Thu 04/16 22Z 0.43 2015  78  32  13 0.00
Thu 04/16 23Z 0.59 2019  82  29  12 0.00
Fri 04/17 00Z 0.59 2024  87  26  13 0.00
Fri 04/17 01Z 0.60 2123  93  90  13 0.06
Fri 04/17 02Z 0.88 2625  92  93  11 0.61
Fri 04/17 03Z 0.80 2626  86  84  11 0.10
Fri 04/17 04Z 0.92 2628  93  81  10 0.02
Fri 04/17 05Z 0.80 2625  91  67  11 0.01
Fri 04/17 06Z 0.72 2623  92  49  11 0.01
Fri 04/17 07Z 0.68 2722  93  40  10 0.01
Fri 04/17 08Z 0.69 2721  95  33  10 0.02
Fri 04/17 09Z 0.65 2821  97  37   9 0.03
Fri 04/17 10Z 0.51 2920  97  39   9 0.03
Fri 04/17 11Z 0.34 3121  97  53   8 0.02
Fri 04/17 12Z 0.12 3423  96  68   7 0.02
Fri 04/17 13Z 0.05 3523  94  73   7 0.01
Fri 04/17 14Z 0.04 3522  92  71   7 0.00
Fri 04/17 15Z 0.06 3520  90  66   7 0.00
Fri 04/17 16Z 0.06 3518  89  69   7 0.00
Fri 04/17 17Z 0.07 3517  88  61   7 0.00
Fri 04/17 18Z 0.07 3516  88  51   8 0.00
Fri 04/17 19Z 0.06 3516  86  42   8 0.00
Fri 04/17 20Z 0.05 3516  84  26   8 0.00
Fri 04/17 21Z 0.08 3516  80  17   8 0.00
Fri 04/17 22Z 0.11 0015  77  10   8 0.00
Fri 04/17 23Z 0.14 0014  73   8   8 0.00
Sat 04/18 00Z 0.18 0213  69   7   9 0.00
Sat 04/18 01Z 0.19 0311  66   5   9 0.00
Sat 04/18 02Z 0.19 0410  65   5   9 0.00
Sat 04/18 03Z 0.18 0508  63   5   9 0.00
Sat 04/18 04Z 0.18 0607  65   5   9 0.00
Sat 04/18 05Z 0.17 1008  68   4   9 0.00

Run total areal avg QPF for the Central_Greens is: 1.35 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