NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260326_0000
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 03/26 00Z 0.17 1817  49  69  -2 0.00
Thu 03/26 01Z 0.41 1823  49  66  -2 0.00
Thu 03/26 02Z 0.64 1927  54  90  -1 0.00
Thu 03/26 03Z 1.62 2032  70  91  -2 0.00
Thu 03/26 04Z 0.75 2135  92  91  -2 0.02
Thu 03/26 05Z 0.86 2233  85  94  -1 0.01
Thu 03/26 06Z 0.75 2133  75  96   0 0.00
Thu 03/26 07Z 0.76 2235  66  95   0 0.00
Thu 03/26 08Z 0.73 2233  66  95   0 0.00
Thu 03/26 09Z 0.83 2334  71  93   0 0.00
Thu 03/26 10Z 0.76 2432  90  93   0 0.01
Thu 03/26 11Z 0.72 2430  88  92   0 0.01
Thu 03/26 12Z 0.65 2429  84  95   2 0.02
Thu 03/26 13Z 0.72 2432  86  94   2 0.03
Thu 03/26 14Z 0.77 2432  84  82   2 0.02
Thu 03/26 15Z 0.76 2530  80  44   2 0.01
Thu 03/26 16Z 0.83 2528  75  45   3 0.00
Thu 03/26 17Z 0.95 2526  76  64   3 0.00
Thu 03/26 18Z 1.14 2525  77  75   2 0.00
Thu 03/26 19Z 1.39 2523  76  84   3 0.00
Thu 03/26 20Z 1.21 2521  82  94   2 0.02
Thu 03/26 21Z 0.85 2517  83  95   3 0.04
Thu 03/26 22Z 0.49 2611  84  95   3 0.04
Thu 03/26 23Z 0.36 2809  96  96   1 0.15
Fri 03/27 00Z 0.20 3207  94  99   2 0.07
Fri 03/27 01Z 0.22 3114  96  98   1 0.19
Fri 03/27 02Z 0.08 3411  94  99   2 0.08
Fri 03/27 03Z 0.10 3315  95  99   1 0.08
Fri 03/27 04Z 0.21 3217  97  98   0 0.03
Fri 03/27 05Z 0.23 3220  97  92   0 0.02
Fri 03/27 06Z 0.28 3225  97  93  -3 0.02
Fri 03/27 07Z 0.31 3227  96  57  -4 0.02
Fri 03/27 08Z 0.25 3326  96   4  -5 0.01
Fri 03/27 09Z 0.25 3328  96   2  -8 0.01
Fri 03/27 10Z 0.23 3329  95   1  -9 0.00
Fri 03/27 11Z 0.23 3329  94   1 -11 0.00
Fri 03/27 12Z 0.19 3329  85   2 -11 0.00
Fri 03/27 13Z 0.16 3327  72   4 -11 0.00
Fri 03/27 14Z 0.14 3325  64   4 -11 0.00
Fri 03/27 15Z 0.12 3323  59   2 -12 0.00
Fri 03/27 16Z 0.10 3420  57   2 -12 0.00
Fri 03/27 17Z 0.19 3417  60   2 -13 0.00
Fri 03/27 18Z 0.50 3314  60   3 -13 0.00
Fri 03/27 19Z 0.85 3313  55   3 -13 0.00
Fri 03/27 20Z 0.93 3212  48   4 -13 0.00
Fri 03/27 21Z 0.28 3313  41   5 -12 0.00
Fri 03/27 22Z 0.15 3312  39   6 -12 0.00
Fri 03/27 23Z 0.16 3211  44   7 -11 0.00
Sat 03/28 00Z 0.16 3210  51   8 -11 0.00
Sat 03/28 01Z 0.13 3210  56   9 -11 0.00
Sat 03/28 02Z 0.15 3210  62   9 -12 0.00
Sat 03/28 03Z 0.14 3210  65   8 -12 0.00
Sat 03/28 04Z 0.10 3210  65   6 -12 0.00
Sat 03/28 05Z 0.07 3309  67   8 -13 0.00
Sat 03/28 06Z 0.06 3310  66   9 -13 0.00
Sat 03/28 07Z 0.10 3310  63  11 -14 0.00
Sat 03/28 08Z 0.11 3211  60  18 -14 0.00
Sat 03/28 09Z 0.10 3310  59  20 -15 0.00
Sat 03/28 10Z 0.09 3309  59  29 -15 0.00
Sat 03/28 11Z 0.09 3309  63  42 -15 0.00

Run total areal avg QPF for the Central_Greens is: 0.91 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